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COMPARATIVE ZOOLOGY 


Structural and Systematic 


FOR USE IN SCHOOLS AND COLLEGES 


By JAMES ORTON, A.M., Ph.D. 

H 

LATE PROFESSOR OF NATURAL HISTORY IN VASSAR COLLEGE; CORRESPONDING MEMBER 
OF THE ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, AND OF THE 
LYCEUM OF NATURAL HISTORY, NEW YORK; AUTHOR 
OF “THE ANDES AND THE AMAZON,” ETC. 


REVISED EDITION 

r 


The education of a naturalist now consists chiefly in learning how to 
compare. ’ ’— Ag a ssi z. 


NEW YORK 

HARPER k BROTHERS, FRANKLIN SQUARE 

1 893 


Entered according to Act of Congress, in the year 1876, by 
HARPER & BROTHERS, 

In the Office of the Librarian of Congress, at Washington. 


Copyright, 1883, by Harper & Brothers. 


L.' .alN’GB 

7 

APR 23 1842 

A S 


ACCESSIONS DIV1SI05 



tuo 



PREFACE. 


The distinctive character of this work consists in the 
treatment of the whole Animal Kingdom as a unit; in 
the comparative study of the development and variations 
of organs and their functions, from the simplest to the 
most complex state; in withholding Systematic Zoology 
until the student has mastered those structural affinities 
upon which true classification is founded; and in being 
fitted for High Schools and Mixed Schools by its lan¬ 
guage and illustrations, yet going far enough to constitute 
a complete grammar of the science for the undergraduate 
course of any College. 

It is designed solely as a manual for instruction. It is 
not a work of reference, nor a treatise. So far as a book 
is encyclopedic, it is unfit for a text-book. This is pre¬ 
pared on the principle of “ just enough, and no more.” 
It aims to present clearly, and in a somewhat new form, 
the established facts and principles of Zoology. All the¬ 
oretical and debatable points, and every fact or statement, 
however valuable, which is not absolutely necessary to a 
clear and adequate conception of the leading principles, 
are omitted. It is written in the light of the most recent 
phase of the science, but not in the interest of any par¬ 
ticular theory. To have given an exhaustive survey of 
animal life would have been not only undesirable, but 
impossible. Even Cuvier’s great work must be supple- 




IV 


PREFACE. 


mented by museums, monographs, and microscopes. Nat¬ 
ural History has outgrown the limits of a single book. 
TriaLhas proved the folly of giving the student so many 
things to learn that he has no time to understand, and the 
error of condemning the student to expend his strength 
upon the details of classification, which may change in 
the coming decade, instead of upon structure, w T hich is 
permanent. Of course, specialists will miss many things, 
and find abundant room for criticism in what they regard 
as deficiencies; but the work should be judged by what 
it does contain, rather than by what it does not. 

What is claimed, in the language of inventors, is the 
selection and arrangement of essential principles and 
typical illustrations from the standpoint of the teacher. 
The synthetic method is employed, as being the most 
natural: to begin with complex Man, instead of the sim¬ 
plest forms, would give a false idea. Man is not a model, 
but a monstrosity, the most modified of Vertebrates. 
But these outlines must be filled up, on the part of the 
teacher, by lectures, and by the exhibition of specimens; 
and, on the part of the student, by observation (noting, 
above all, the characteristic habits of animals), and by per¬ 
sonal work with the knife and microscope. No text-book 
can take the place of nature, or supersede oral instruction 
from a competent teacher. 

Suggestions and corrections from naturalists and teach¬ 
ers will be thankfully received. 

In a work of this character, which is but a compound 
of the labors of all naturalists, it w r ould be superfluous to 
make acknowledgments. The works referred to on page 
397 have been specially consulted. 


REVISER’S NOTE. 


In revising the work of Professor Orton, the writer has 
not attempted to rewrite the book nor to introduce new 
ideas.' His plan has been to insert such changes as the 
author would have been likely to make if he had lived to 
revise his book. On only two points has the reviser de¬ 
parted from this plan of altering only minor details. The 
chapter on Development has been largely rewritten, and 
the classification of the Invertebrates has been changed 
so as to separate the worms from the Arthropoda and 
the sponges from the Protozoa. In both these cases the 
change seemed imperatively demanded by the progress of 
Zoology in those directions. It is hoped that the altera¬ 
tions in the book will increase its accuracy and useful¬ 
ness. 

Edw. A. Biege. 


University of Wisconsin. 

































I 


CONTENTS. 


INTRODUCTION. 

PAGE 


Definition of Zoology, and its Place among the Sciences. 11 

Historical Sketch. 14 


PART I.—STRUCTURAL ZOOLOGY. 


CHAPTER I. 

Minerals and Organized Bodies Distinguished 

CHAPTER II. 

Plants and Animals Distinguished. 

CHAPTER III. 


Relation between Minerals, Plants, and Animals 

CHAPTER IV. 


Life. .. 


CHAPTER V. 

Organization. 

1. Cells.. 

2. Tissues. . 

3. Organs, and their Functions. 


Nutrition 


CHAPTER VI. 


CHAPTER VII. 


19 


21 


27 


28 


30 

31 

32 
41 


45 


The Food of Animals. 


47 

















CONTENTS. 


viii 

CHAPTER VIII. page 

How Animals Eat. 41) 

1. The Prehension of Food. 49 

2. The Mouths of Animals. 55 

3. The Teeth of Animals. 03 

4. Deglutition, or How Animals Swallow . 72 

CHAPTER IX. 

The Alimentary Canal. 74 

CHAPTER X. 

How Animals Digest.. 91 

CHAPTER XI. 

The Absorbent System .. . 94 

CHAPTER XII. 

Tiie Blood of Animals . 97 

CHAPTER XIII. 

The Circulation of the Blood. 103 

CHAPTER XIV. 

How Animals Breathe . Ill 

CHAPTER XV. 

Secretion and Excretion. 121 

CHAPTER XVI. 

The Skin and Skeleton.. 127 

CHAPTER XVII. 

How Animals Move. . 154 

1. Muscle. 154 

2. Locomotion. 157 

CHAPTER XVIII. 

T he Nervous System. 166 

1. The Senses. 176 

2. Instinct and Intelligence... 184 

3. The Voices of Animals. 188 






















CONTENTS. 


is 


CHAPTER XIX. page 

Reproduction... 191 

CHAPTER XX. 

Development. 197 

1. Metamorphosis . 207 

2. Alternate Generation. 21 L 

3. Growth and Repair. 214 

4. Likeness and Variation. 215 

5. Homology, Analogy, and Correlation . 217 

6. Individuality . 220 

7. Relations of Number, Size, Form, and Rank. 221 

8. The Struggle for Life. 226 


PART II.—SYSTEMATIC ZOOLOGY. 

CHAPTER XXI. 

The Classification op Animals . 231 

Protozoa... 238 

Spongida. 244 

Ccelenterata. 246 

Echinodermata. 257 

Vermes. 263 

Mollusea.. . 269 

Arthropoda. . 281 

Tunicata... 305 

Vertebrata. . 306 

CHAPTER XXII. 

Systematic Arrangement of Representative Forms . 362 

CHAPTER XXIII. 

The Distribution of Animals. 371 


NOTES . 381 

THE NATURALIST’S LIBRARY.. 397 


INDEX 


399 






























The first thing to be determined about a new specimen is not its name, 
but its most prominent character. Until you know an animal, care not for 
its name.— Agassiz. 

The great benefit which a scientific education bestows, whether as train¬ 
ing or as knowledge, is dependent upon the extent to which the mind of the 
student is brought into immediate contact with facts—upon the degree to 
which he learns the habit of appealing directly to Nature.— Huxley. 



INTRODUCTION. 


1. Definition of Zoology, and its Place among the 
Sciences. —The province of Natural History is to describe, 
compare, and classify natural objects. These objects have 
been divided into the “ organic ” and the “ inorganic,” or 
those which are, and those which are not, the products of life. 
Biology is the science of the former, and Mineralogy the sci¬ 
ence of the latter. Biology again separates into Botany , or the 
Natural History of Plants, and Zoology , or the Natural His¬ 
tory of Animals ; while Mineralogy divides into Mineralogy 
proper , the science of mineral species, and Lithology , the 
science of mineral aggregates or rocks. Geology is that com¬ 
prehensive knowledge of the earth’s structure and develop¬ 
ment which rests on the whole doctrine of Natural History. 

If we examine a piece of chalk, and determine its physical 
and chemical characters, its mode of occurrence and its uses, 
so as to distinguish it from all other forms of matter, we 
have its Mineralogy. But chalk occurs in vast natural beds : 
the examination of these masses—their origin, structure, po¬ 
sition, and relation to other rocks—is the work of the Li¬ 
thologist. Further, we observe that while chalk and marble 
are chemically alike, they widely differ in another respect. 
Grinding a piece of chalk so thin that we can see through 
it, and putting it under a microscope, we find imbedded in it 
innumerable bodies, about the hundredth of an inch in diame¬ 
ter, having a well-defined, symmetrical shape, and chambered 
like a Nautilus. We cannot say these are accidental aggre¬ 
gations, nor are they crystals : if the oyster-shell is formed 
by an oyster, these also must be the products of life. In¬ 
deed, the dredge brings up similar microscopic skeletons 
from the bottom of the Atlantic. So we conclude that chalk 
is but the dried mud of an ancient sea, the cemetery of count* 



12 


INTRODUCTION. 


less animals that lived and died long ago. The considera¬ 
tion of their fossil remains belongs to Paleontology, or that 
part of Biology which describes the relics of extinct forms 
of life. To study the stratigraphical position of the chalk- 
bed, and by the aid of its Paleontology to determine its age 
and part in the world’s history, is the business of Geology. 

Of all the sciences, Zoology is the most extensive. Its 
field is a world of varied forms—hundreds of thousands in 
number. To determine their origin and development, their 
structure, habits, distribution, and mutual relations, is the 
work of the Zoologist. But so many and far-reaching are 
the aspects under which the animal creation may be contem¬ 
plated, that the general science is beyond the grasp of any 
single person. Special departments have, therefore, arisen ; 
and Zoology, in its comprehensive sense, is the combined re¬ 
sult of the labors of many workers, each in his own line of 
research. 

Structural Zoology treats of the organization of animals. 
There are two main branches : Anatomy , which considers 
the constitution and construction of the animal frame ; and 
Physiology , which is the study of the apparatus in action. 
The former is separated into Embryology , or an account of 
the successive modifications through which an animal passes 
in its development from the egg to the adult state ; and 
Morphology , which includes all inquiries concerning the form 
of mature animals, or the form and arrangement of their or¬ 
gans. The microscopical examination of any part, especial¬ 
ly the tissues, belongs to Histology. Comparative Zoology 
is the comparison of the anatomy and physiology of all ani¬ 
mals, existing and extinct, to discover the fundamental like¬ 
ness underneath the superficial differences, and to trace the 
adaptation of organs to the habits and spheres of life. It is 
this comparative science which has led to such grand gen¬ 
eralizations as the unity of structure amidst the diversity of 
form in the animal creation, and by revealing the degrees of 
affinity between species has enabled us to classify them in 
natural groups, and thus laid the foundation of Systematic 
Zoology. When the study of structure is limited to a par¬ 
ticular class or species of animals, or to a particular organ 
or part, monographic sciences are created, as Ornithotomy , 


INTRODUCTION. 13 

or anatomy of birds ; Osteology , or the science of bones; 
and Odontography , or the natural history of teeth. 

Systematic Zoology is the classification or grouping of ani¬ 
mals according to their structural and developmental rela¬ 
tions. The systematic knowledge of the several classes, 
as Insects, Reptiles, and Birds, has given rise to subordinate 
sciences, like Entomology , Herpetology , or Ornithology .** 

Distributive Zoology is the knowledge of the successive ap¬ 
pearance of animals in the order of time (Paleontology in 
part), and of the geographical and physical distribution of 
animals, living or extinct, over the surface of the earth. 

Theoretical Zoology includes those provisional modes of 
grouping facts, and interpreting them, which still stand 
waiting at the gate of science. They may be true, but we 
cannot say that they are true. The evidence is incomplete. 
Such are the theories which attempt to explain the origin of 
life and the origin of species. 

Suppose we wish to understand all about the Horse. Our 
first object is to study its structure. The whole body is en¬ 
closed within a hide, a skin covered with hair ; and if this 
hide be taken off, we find a great mass of flesh or muscle, 
the substance which, by its power of contraction, enables 
the animal to move. On removing this, we have a series of 
bones, bound together with ligaments, and forming the skel¬ 
eton. Pursuing our researches, we find within this frame¬ 
work two main cavities : one, beginning in the skull and 
running through the spine, containing the brain and spinal 
marrow ; the other, commencing with the mouth, contains 
the gullet, stomach, intestines, and the rest of the apparatus 
for digestion, and also the heart and lungs. Examinations 
of this character would give us the Anatomy of the Horse, 
or, more precisely, Hippotomy. The study of the bones 
alone would be its Osteology; the knowledge of the nerves 
would belong to Neurotomy. If we examined, under the 
microscope, the minute structure of the hair, skin, flesh, 
blood, and bone, we would learn its Histology. The consid¬ 
eration of the manifold changes undergone in developing 
from the egg to the full-grown animal, would be the Embry- 


* Numbers like this refer to the Notes at the end of the volume. 




14 


INTRODUCTION. 


ology of the Horse ; and its Morphology , the special study 
of the form of the adult animal and of its internal organs. 

Thus far we have been looking, as it were, at a steam- 
engine, with the fires out, and nothing in the boiler ; but the 
body of the living Horse is a beautifully formed, active ma¬ 
chine, and every part has its different work to do in the 
working of that machine, which is what we call its life. 
The science of such operations as the grinding of the food 
in the complex mill of the mouth ; its digestion in the labo¬ 
ratory of the stomach ; the pumping of the blood through a 
vast system of pipes over the whole body; its purification 
in the lungs ; the process of growth, waste, and repair ; and 
that wondrous telegraph, the brain, receiving impressions, 
sending messages to the muscles, by which the animal is en¬ 
dowed with voluntary locomotion—this is Physiology. But 
Horses are not the only living creatures in the world ; and 
if we compare the structures of various animals, as the Horse, 
Zebra, Dog, Monkey, Eagle, and Codfish, we shall find more 
or less resemblances and differences, enough to enable us to 
classify them, and give to each a description which will dis¬ 
tinguish it from all others. This is the work of Systematic 
Zoology. Moreover, the Horses now living are not the only 
kinds that have ever lived ; for the examination of the 
earth’s crust—the great burial-ground of past ages—reveals 
the bones of numerous horse-like animals : the study of this 
pre-adamite race belongs to Paleontology. The chronologi¬ 
cal and geographical distribution of species is the depart¬ 
ment of Distributive Zoology. Speculations about the ori¬ 
gin of the modern Horse, whether by special creation, or by 
development from some allied form now extinct, are kept 
aloof from demonstrative science, under the head of Theo¬ 
retical Zoology. 

2. History.—The Greek philosopher Aristotle (b.c. 384- 
322) is called the “ Father of Zoology.” Certainly, he is the 
only great representative in ancient times, though his fre¬ 
quent allusions to familiar works on anatomy show that 
something had been done before him. His “History of 
Animals,” in nine books, displays a wonderful knowledge of 
external and internal structure, habits, instincts, and uses. 
His descriptions are incomplete, but generally exact, so far 


INTRODUCTION. 


15 


as they go. Alexander, it is said, gave him nine hundred 
talents to collect materials, and put at his disposal several 
thousand men, for hunting specimens and procuring infor¬ 
mation. 

The Romans accomplished little in natural science, though 
their military expeditions furnished unrivalled opportuni¬ 
ties. Nearly three centuries and a half after Aristotle, Pliny 
(a.d. 23-79) wrote his “Natural History.” He was a volu¬ 
minous compiler, not an observer : he added hardly one new 
fact. He states that his work was extracted from over two 
thousand volumes, most of which are now lost. 

During the Middle Ages, Natural History was studied in 
the books of the ancients; and at the close of the fifteenth 
century it was found where Pliny had left it, with the addi¬ 
tion of many vague hypotheses and silly fancies. Albertus 
Magnus, of the thirteenth century, and Conrad Gesner and 
Aldrovandus, of the sixteenth, were voluminous writers, not 
naturalists. In the latter half of the sixteenth century, men 
began to observe nature for themselves. The earliest note¬ 
worthy researches were made on Fishes, by Rondelet (1507- 
1556) and Belon (1517-1564), of France, and Salviani (1514- 
1572), of Italy. They were followed by valuable observa¬ 
tions upon Insects, by Redi (1626-1698), of Italy, and Swam¬ 
merdam (1637-1680), of Holland ; and towards the end of 
the same century, the Dutch naturalist, Leeuwenhoeck 
(1632-1723), opened a new world of life by the use of the 
microscope. 

But there was no real advance of Systematic Zoology till 
the advent of the illustrious John Ray (1628-1705), of Eng¬ 
land. His “ Synopsis,” published in 1693, contained the first 
attempt to classify animals according to structure. Ray was 
the forerunner of “the immortal Swede,” Linnaeus (1707- 
1778), “the great framer of precise and definite ideas of 
natural objects, and terse teacher of the briefest and clearest 
expressions of their differences.” His chief merit was in de¬ 
fining generic groups, and inventing specific names. 3 Scarce¬ 
ly less important, however, was the impulse which he gave 
to the pursuit of Natural History. The spirit of inquiry, 
which his genius infused among the great, produced voyages 
of research, which led to the formation of national museums. 


16 


INTRODUCTION. 


The first expedition was sent forth by George III. of Eng¬ 
land, in 1765. Reaumur ( 1683-1757) made the earliest 
zoological collection in France ; and the West Indian col¬ 
lections of Sir Hans Sloane (1660-1752) were the nucleus of 
the British Museum. The accumulation of specimens sug¬ 
gested comparisons, which eventually resulted in the high¬ 
est advance of the science. 

The brilliant style of Buff on (1707-1788) made Zoology 
popular not only in France, but throughout Europe. While 
the genius of Linnaeus led to classification, that of Buffon 
lay in description. He was the first to call attention to the 
subject of Distribution. Lamarck (1745-1829), of Paris, 
was the next great light. The publication of his “ Animaux 
sans Vertebres,” in 1801, was an epoch in the history of the 
lower animals. He was also the first prominent advocate of 
the transmutation of species. 

But the brightest luminary in Zoology was George Cuvier 
(1769-1832), a German, born on French soil. Before his 
time, “ there was no great principle of classification. Facts 
were accumulated, and more or less systematized, but they 
were not yet arranged according to law ; the principle was 
still wanting by which to generalize them and give meaning 
and vitality to the whole.” It was Cuvier who found the 
key. He was the first so to interpret structure as to be able 
from the inspection of one bone to reconstruct the entire 
animal, and assign its position. Ilis anatomical investiga¬ 
tions revealed the natural affinities of animals, and led to the 
grand generalization, that the most comprehensive groups 
in the kingdom were based, not on special characters, but on 
different plans of structure. Palissy had long ago (1580) 
asserted that petrified shells were of animal origin ; but the 
publication of Cuvier’s “ Memoir on Fossil Elephants,” in 
1800, was the beginning of those profound researches on the 
remains of ancient life which created Paleontology. The 
discovery of the true relation between all animals, living 
and extinct, opened a boundless field of inquiry ; and from 
that day the advance of Zoology has been unparalleled. 
Special studies of particular parts or classes of animals have 
so rapidly developed, that the history of Zoology during the 
last fifty years is the history of many sciences. 3 


PART I. 


STRUCTURAL ZOOLOGY. 







COMPARATIVE ZOOLOGY, 


CHAPTER I. 

MINERALS AND ORGANIZED BODIES DISTINGUISHED. 

Nature may be separated into two great kingdoms— 
that of mere dead matter, and that of matter under the 
influence of life. 4 These differ in the following points: 

(1) Composition.— While most of the chemical elements 
are found in different living beings, by far the greater 
part of their substance is composed of three or four—car¬ 
bon, oxygen, and hydrogen ; or these three with the addi¬ 
tion of nitrogen. Next to these elements, sulphur and 
phosphorus are most widely distributed, though always 
found in very small quantities. The organic compounds 
belong to the carbon series, and contain three, four, or 
five elements. The former class, comprising starch, sugar, 
fat, etc., are relatively stable. The latter, possessing the 
three elements named, with nitrogen and sulphur or phos¬ 
phorus, are very complex, containing a very large number 
of atoms to the molecule, and are usually unstable. Here 
belong albumen, myosin, chondrin, etc., the constituents 
of the living tissues. The formula for albumen is said to 
be C 72 H 112 N 18 S0 22 , or some multiple of this formula. 
These compounds also contain more or less water, and 
usually exist in a jelly-like condition, neither solid nor 
fluid. With these colloid substances alone is life associ¬ 
ated. Only these can undergo the rapid decomposition 



20 


COMPARATIVE ZOOLOGY. 


and recomposition necessary to the manifestation of the 
vital phenomena. 

(2) Structure. —Minerals are homogeneous, while organ¬ 
ized bodies are usually heterogeneous; i. e., composed of 
different parts, called tissues and organs, having peculiar 
uses and definite relations to one another. The tissues 
and organs, again, are heterogeneous, consisting mainly of 
microscopic cells, structures developed only by vital ac¬ 
tion. All the parts of an organism are mutually depend¬ 
ent, and reciprocally means and ends, while each part of a 
mineral exists for itself. The smallest fragment of mar¬ 
ble is as much marble as a mountain-mass; but the frag¬ 
ment of a plant or animal is not an individual. 

(3) Size and Shape.— Living bodies gradually acquire de¬ 
terminate dimensions; so do minerals in their perfect or 
crystal condition. But uncrystallized, inorganic bodies 
have an indefinite bulk. Most minerals are amorphous; 
crystals have regular forms, bounded, as a rule, by plane 
surfaces and straight lines; plants and animals are cir¬ 
cumscribed by curved surfaces, and rarely assume accurate 
geometrical forms. 5 

(4) Phenomena.— Minerals remain internally at rest, and 
increase by external additions, if they grow at all. Liv¬ 
ing beings are constantly changing the matter of which 
they are composed, and grow by taking new matter into 
themselves and placing it among the particles already 
present. Organized bodies, moreover, pass through a cy¬ 
cle of changes—growth, development, reproduction, and 
death. These phenomena are characteristic of living as 
opposed to inorganic bodies. All living bodies grow from 
within, constantly give up old matter and replace it by 
new, reproduce their kind, and die; and no inorganic 
body shows any of these phenomena. 


PLANTS AND ANIMALS DISTINGUISHED. 


21 


CHAPTER II. 

PLANTS AND ANIMALS DISTINGUISHED. 

It may seem an easy matter to draw a line between 
plants and animals. Who cannot tell a Cow from a Cab¬ 
bage ? Who would confound a Coral with a Mushroom ? 
Yet it is impossible to assign any absolute, distinctive 
character which will divide the one mode of life from 
the other. The difficulty of defining an animal increases 
with our knowledge of its nature. Linnaeus defined it in 
three words; a century later, Owen declared that a defi¬ 
nition of plants which would exclude all animals, or of 
animals which would not let in a single plant, was impos¬ 
sible. Each different character used in drawing the boun¬ 
dary will bisect the debatable ground in a different lati¬ 
tude of the organic world. Between the higher animals 
and higher plants the difference is apparent; but when 
we reflect how many characters the two have in common, 
and especially when we descend to the lower and minuter 
forms, we discover that the two “kingdoms” touch, and 
even dissolve into, each other. This border-land has been 
as hotly contested among naturalists as many a disputed 
frontier between adjacent nations. Its inhabitants have 
been taken and retaken several times by botanists and 
zoologists; for they have characters that lead on the one 
side to plants, and on the other to animals. To solve the 
difficulty, some eminent naturalists, as Hackel and Owen, 
propose a fourth “ kingdom,” to receive those living be¬ 
ings which are organic, but not distinctly vegetable or 
animal. But a greater difficulty arises in attempting to 
fix its precise limits. 


22 COMPARATIVE ZOOLOGY. 

The drift of modern research points to this: that there 
are but two kingdoms of nature, the mineral and the or¬ 
ganized, and these closely linked together; that the lat¬ 
ter must be taken as one whole, from which two great 
branches rise and diverge. “ There is at bottom but one 
life, which is the whole life of some creatures, and the 
common basis of the life of all; a life of simplest moving 
and feeling, of feeding and breathing, of producing its 
kind and lasting its day: a life which, so far as we at 
present know, has no need of such parts as we call organs. 
Upon this general foundation are built up the manifold 
special characters of animal and vegetable existence; but 
the tendency, the endeavor, so to speak, of the plant is 
one, of the animal is another, and the unlikeness between 
them widens the higher the building is carried up. As 
we pass along the series of either [branch] from low to 
high, the plant becomes more vegetative, the animal more 
animal.” 6 

Defining animals and plants by their prominent char¬ 
acteristics, we may say that a living being which has cell- 
walls of cellulose, and by deoxidation and synthesis of its 
simple food-stuffs produces the complicated organic sub¬ 
stances, is a plant; while a living being which has albu¬ 
minous tissues, and by oxidation and analysis reduces its 
complicated food-stuffs to a simpler form, is an animal. 
But both definitions are defective, including too many 
forms, and excluding forms that properly belong to the 
respective kingdoms. No definition is possible which 
shall include all animals and exclude all plants, or vice 
versa. 

(l) Origin.— Both branches of the tree of life start alike: 
the lowest of plants and animals, as Protococcus and Ore- 
garina , consist of a single cell. In fact, the cycle of life 
in all living beings, high or low, begins in a small, round 
particle of matter—in plants called an ovule, in animals 


PLANTS AND ANIMALS DISTINGUISHED. 


23 


an ovum. This cell contains a semi-fluid, called proto¬ 
plasm, similar in composition and in function. In the 
very simplest forms the protoplasm is not enclosed by a 
membrane, but generally there is a cell-wall. In plants, 
with few exceptions, this wall is of cellulose, a substance 
akin to starch; in animals, with few exceptions, the wall 
is a pellicle of firmer protoplasm, i. e., albuminous. 

(2) Composition.— Modern research has broken down the 
partition between plants and animals, so far as chemical 
nature is concerned. The vegetable fabric and secretions 
may be ternary or binary compounds; but the essential 
living parts of plants, as of animals, are quaternary, con¬ 
sisting of four elements—carbon, hydrogen, oxygen, and 
nitrogen. Cellulose (woody fibre), starch, and chlorophyl 
(green coloring matter) are eminently vegetable products, 
but not distinctive; for cellulose is wanting in some plants, 
as some Fungi, and present in some animals, as Tunicates; 
starch, under the name of glycogen, is found in the liver 
and brains of Mammals, and chlorophyl gives color to the 
fresh - water Polyp. Still, it holds good, generally, that 
plants consist mainly of cellulose, dextrine, and starch; 
while animals are mainly made up of albumen, fibrine, 
and gelatine; that nitrogen is more abundant in animal 
tissues, while in plants carbon is predominant. 

(3) Form. —~No outline can be drawn which shall be com¬ 
mon to all animals or all plants. The lowest members of 
both have no fixed shape. The spores of Confervse can 
hardly be distinguished from animalcules; the compound 
and fixed animals, Sea-mat and Sea-moss (Polyzoa), and 
Corals, often resemble vegetable forms, although in struct¬ 
ure widely removed from plants. Similar conditions of 
life are here accompanied by an external likeness. In 
free-living animals this resemblance is not found. 

(4) Structure. —A plant is the multiplication of the unit 
—a cell with a cellulose wall. Some simple animals have 


24 


COMPARATIVE ZOOLOGY. 


a similar simple cellular structure; and all animal tissues, 
while forming, are cellular. But this character, which is 
permanent in plants, is generally transitory in animals. 
In the more highly organized tissues the cells are so united 
as partly or wholly to lose their individuality, and the 
characteristic part of the tissue is the intercellular sub¬ 
stance, while the cells themselves are small and unimpor¬ 
tant, or else the cells are melted together and lose their 
dividing walls, as in striped muscles and in nerves. Ex¬ 
cepting the lowest forms, animals are more composite than 
plants, i. e., their organs are more complex and numerous, 
and more specially devoted to particular purposes. Rep¬ 
etition of similar parts is a characteristic of plants; and 
when found in animals, as the Angle-worm, is called vege¬ 
tative repetition. Differentiation and specialization are 
characteristic of animals. Most animals, moreover, have 
fore-and-aft polarity; in contrast, plants are up-and-down 
structures, though in this respect they are imitated by 
radiated animals, like the Star-fish. Plants are continually 
receiving additional members; most animals soon become 
perfect. 

(5) Physiology.— In their modes of nutrition, plants and 
animals stand widest apart. A plant in the seed and an 
animal in the egg exist in similar conditions: in both 
cases a mass of organic matter accompanies the germ. 
When this supply of food is exhausted, both seek nourish¬ 
ment from without. But here analogy ends: the plant 
feeds on mineral matter, the animal on organic. Plants 
have the power to form chlorophyl, the green coloring 
matter of leaves, which uses the force of the sunlight to 
form starch out of the inorganic substances—carbon-di¬ 
oxide and water. They are able also to form albuminoid 
matter out of inorganic substances. A very few animals 
which have a substance identical with or allied to chloro¬ 
phyl have the same power, 7 but in general animals are de- 


PLANTS AND ANIMALS DISTINGUISHED. 


25 


pendent for their food on the compounds put together in 
plants. Colorless plants, possessing no chlorophyl, feed, 
like animals, on organic compounds. No living being is 
able to combine the simple elements—carbon, oxygen, hy¬ 
drogen, and nitrogen—into organic compounds. 

The food of plants is gaseous (carbon dioxide and am¬ 
monia) or liquid (water), that of animals usually more or 
less solid. The plant, then, absorbs these foods through 
its outer surface, while the animal takes its nourishment 
in larger or smaller masses, and digests it in a special cav¬ 
ity. A few’ exceptions, however, occur on both sides. 
Certain moulds seem to swallow their food, and certain 
animals, as the tape-worm, have no digestive tract. 

Plants are ordinarily fixed, their food is brought to 
them, and a large share of their work, the formation of 
organic compounds, is done by the force of the sunlight; 
w T hile animals are usually locomotive, must seek their 
food, and are unable to utilize the general forces of nature 
as the plant does. The plant is thus able to grow much 
more than the animal, as very little of the nourishment 
received is used to repair waste, while in most animals the 
time soon comes when waste and repair are approximately 
equal. But in both all work done is paid for by waste of 
substance already formed. 

In combining carbon dioxide and water to form starch 
the plant sets oxygen free (6(C0 2 ) + 5(H 2 0) = C 6 H 10 O 5 + 
6(0 2 )): in oxidizing starch or other food the animal uses 
oxygen and sets carbon dioxide free. The green plant in 
the sunlight, then, gives off oxygen and uses carbon diox¬ 
ide, while plants which have no chlorophyl, at all times, 
and all plants in the darkness, use oxygen and give off 
carbon dioxide, like an animal. Every plant begins life 
like an animal—a consumer, not a producer: not till the 
young shoot rises above the soil, and unfolds itself to the 
light of the sun, at the touch of whose mystic rays chlo- 


26 


COMPARATIVE ZOOLOGY. 


rophyl is created, does real, constructive vegetation begin; 
then its mode of life is reversed—carbon is retained and 
oxygen set free. 

Most plants, and many animals, multiply by budding 
and division; on both we practise grafting; in both the 
cycle of life comes round again to the ovule or ovum. 
Do annuals flower but to die? Insects lay their eggs in 
their old age. 

Both animals and plants have sensibility. This is one 
of the fundamental physiological properties of proto¬ 
plasm. But in plants the protoplasm is scattered and 
buried in rigid structures: feeling is, therefore, dull. In 
animals, the protoplasm is concentrated into special or¬ 
gans, and so feeling, like electricity rammed into Leyden 
jars, goes off with a flash. 8 Plants never possess conscious¬ 
ness or volition, as the higher animals do. 

The self-motion of animals and the rooted state of plants 
is a very general distinction; but it fails where we need it 
most. It is a characteristic of living things to move. The 
protoplasm of all organisms is unceasingly active. 9 Be¬ 
sides this internal movement, myriads of plants, as well 
as animals, are locomotive. Rambling Diatoms, writhing 
Oscillaria, and the agile spores of Cryptogams crowd our 
waters, their instruments of motion (cilia) being of the 
very same character as in microscopic animals; while 
Sponges, Corals, Oysters, and Barnacles are stationary. 
A contractile vesicle is not exclusively an animal prop¬ 
erty, for the fresh-water Yolvox and Gonium have it. 
The act of muscular contraction in the highest animal is 
due to the same kind of change in the form of the cells of 
the ultimate fibrillae as that which produces the sensible 
motions of plants. The ciliary movements of animals 
and of microscopic plants are pronely similar, and in 
neither case indicate consciousne$flfubr self-determining 
power. 4 


RELATION BETWEEN MINERALS, PLANTS, ETC. 27 


Plauts, as well as animals, need a season of repose. 
Both have their epidemics. On both, narcotic and acrid 
poisons produce analogous results. Are some animals 
warm-blooded? In germination and flowering, plants 
evolve heat—the stamens of the Arum, e . y., showing a 
rise of 20°. In a sense, an Oak has just as much heat as 
an Elephant, only the miserly tree locks up the sunlight 
in solid carbon. 

At present, any boundary of the Animal Kingdom is 
arbitrary. “ Probably life is essentially the same in the 
two kingdoms; and to vegetable life, faculties are super- 
added in the lower animals, some of which are, here and 
there, not indistinctly foreshadowed in plants.” u It must 
be said that there are organisms which at one period of 
their life exhibit an aggregate of phenomena such as to 
justify us in speaking of them as animals, while at another 
they appear to be as distinctly vegetable. 10 


CHAPTEK III. 

RELATION BETWEEN MINERALS, PLANTS, AND ANIMALS. 

There are no independent members of creation: all 
things touch upon one another. The matter of the living 
world is identical with that of the inorganic. The plant, 
feeding on the minerals, carbon dioxide, water, and am¬ 
monia, builds them up into complex organic compounds, 
as starch, sugar, gum, cellulose, albumen, fibrine, caseine, 
and gluten. When the plant is eaten by the animal, these 
substances are used for building up tissues, repairing 
waste, laid up in reserve as glycogen and fat, or oxi¬ 
dized in the blood to produce heat. The albuminoids are 
essential for the formation of tissues, like muscle, nerve, 



28 


COMPARATIVE ZOOLOGY. 


cartilage; but the ternary compounds help in repairing 
waste, while both produce heat. When oxidized, whether 
for work or warmth, these complex compounds break up 
into the simple compounds—water, carbon dioxide, and 
(ultimately) ammonia, and as such are returned to earth 
and air from the animal. Both plant and animal end 
their life by going back to the mineral world: and thus 
the circle is complete—from dust to dust. Carbonate of 
ammonia and water, a blade of grass and a horse, are but 
the same elements differently combined and arranged. 
Plants compress the forces of inorganic nature into chem¬ 
ical compounds; animals liberate them. Plants produce 5 
animals consume. The work of plants is synthesis, a 
building-up; the work of animals is analysis, or destruc¬ 
tion. The tendency in plants is deoxidation; the tenden¬ 
cy in animals is oxidation. Without plants, animals would 
perish; without animals, plants had no need to be. There 
is no plant which may not serve as food to some animal. 


CHAPTER IV. 

LIFE. 

All forces are known by the phenomena which they 
cause. So long as the animal and plant were supposed to 
exist in opposition to ordinary physical forces or indepen¬ 
dently of them, a vital force or principle was postulated 
by which the work of the body was performed. It is now 
known that most, if not all, of the phenomena manifested 
by a living body are due to one or more of the ordinary 
physical forces — heat, chemical affinity, electricity, etc. 
There is no work done which demands a vital force. 

The common modern view is that vitality is simply a 



LIFE. 


29 


collective name for the sum of the phenomena displayed 
by living beings. It is neither a force nor a thing at all, 
but is an abstraction, like goodness or sweetness; or, to 
use Huxley’s expression, to speak of vitality is as if one 
should speak of the horologity of a clock, meaning its 
time-keeping properties. 

A third theory is still possible. The combination of 
elements into organic cells, the arrangement of these cells 
into tissues, the grouping of these tissues into organs, and 
the marshalling of these organs into plans of structure, 
call for some further shaping, controlling power to effect 
such wonderful co-ordination. Moreover, the manifesta¬ 
tion of feeling and consciousness is a mystery which no 
physical hypothesis has cleared up. The simplest vital 
phenomenon has in it something over and above the known 
forces of the laboratory. 11 If the vital machine is given, 
it works by physical forces; but to produce it and keep 
it in order needs, so far as we now know, more than mere 
physical force. To this controlling power we may apply 
the name vitality. 

Life is exhibited only under certain conditions. One 
condition is the presence of a physical basis called proto¬ 
plasm. This substance is found in all living bodies, and, 
so far as we know, is similar in all — a viscid, transpar¬ 
ent, homogeneous, or minutely granular, albuminoid mat¬ 
ter. Life is inseparable from this protoplasm; but it is 
dormant unless excited by some external stimulants, such 
as heat, light, electricity, food, water, and oxygen. Thus, 
a certain temperature is essential to growth and motion; 
taste is induced by chemical action, and sight by luminous 
vibrations. 

The essential manifestations of animal life may be re¬ 
duced to three: contractility; sensibility, or the peculiar 
power of receiving and transmitting impressions; and the 
power of assimilating food. All these powers are pos 


30 


COMPARATIVE ZOOLOGY. 


sessed by protoplasm, and so by all animals: all move, 
feel, and grow. But some of the lowest forms are with¬ 
out the slightest trace of organs; they seem to be as per¬ 
fectly homogeneous and structureless as a drop of jelly. 
They could not be more simple. They are devoid of 
muscles, nerves, and stomach; yet they have all the fun¬ 
damental attributes of life—moving, feeling, and eating. 
It has been supposed that the muscular and nervous mat¬ 
ter is diffused in a molecular form; but all we can say is, 
that the highest power of the microscope reveals no organ¬ 
ized structure whatever— i. e., there are no parts set apart 
for a particular purpose, but a fragment is as good as the 
whole to perform all the functions of life. The animal 
series, therefore, begins with forms that feel without 
nerves, move without muscles, and digest without a stom¬ 
ach : in other words, life is the cause of organization , not 
the result of it. Animals do not live because they are or¬ 
ganized, but are organized because they are alive. 


CHAPTER V. 

ORGANIZATION. 

We have seen that the simplest life is a formless speck 
of protoplasm, without distinctions of structure, and there¬ 
fore without distinctions of function, all parts serving all 
purposes — mouth, stomach, limb, and lung — indiscrimi¬ 
nately. There is no separate digestive cavity, no separate 
respiratory, muscular, or nervous systems. Every part 
will successively feed, feel, move, and breathe. Just as in 
the earliest state of society all do everything, each does 
all. Every man is his own tailor, architect, and lawyer. 
But in the progress of social development the principle of 



ORGANIZATION. 


31 


the division of labor emerges. First comes a distinction 
between the governing and governed classes; then follow 
and multiply the various civil, military, ecclesiastical, and 
industrial occupations. 

In like manner, as we advance in the animal series, we 
find the body more and more heterogeneous and complex 
by a process of differentiation , i. e ., setting apart certain 
portions of the body for special duty. In the lowest 
forms, the work of life is carried on by very simple appara¬ 
tus. 12 But in the higher organisms every function is per¬ 
formed by a special organ. For example, contractility, 
at first the property of the entire animal, becomes centred 
in muscular tissue; respiration, which in simple beings 
is effected by the whole surface, is specialized in lungs 
or gills; sensibility, from being common to the whole or¬ 
ganism, is handed over to the nerves. An animal, then, 
whose body, instead of being uniform throughout, is made 
up of different parts for the performance of particular 
functions, is said to ie organized. And the term is as ap¬ 
plicable to the slightly differentiated cell as to complex 
Man. Organization is expressed by single cells, or by 
their combination into tissues and organs. 

1 . Cells.—A cell is the simplest form of organized life. 
In general, it is a microscopic globule, consisting of a del¬ 
icate membrane enclosing a minute por¬ 
tion of protoplasm. The very simplest 
kinds are without granules or signs of 
circulation; but usually the protoplasm 
is granular, and contains a defined sep¬ 
arate mass called the nucleus , within 
which are sometimes seen one or two, 

Fig. 1.—Parts of a Cell: 

rarely more, dark, round specks, named <*, t>,y, ceii-waii ; *>,nu- 
nucleoli. The enveloping membrane is cleus ’ w ’ micleolus ‘ 
extremely thin and transparent, and structureless: it is 
only an excretion of dead matter acting as a boundary to 



32 


COMPARATIVE ZOOLOGY. 


the cell-contents. 13 The nucleus is generally attached to 
the inside of the membrane, and is the centre of activity. 

Cells vary greatly in size, but are generally invisible to 
the naked eye, ranging from to Trrinnr an inch in 
diameter. About 4000 of the smallest would be necessary 
to cover the dot of this letter i. The natural form of iso¬ 
lated cells is spherical; but when they crowd each other, 
as seen in bone, cartilage, and muscle, their outlines be¬ 
come angular, either hexagonal or irregular. 

Within the narrow boundary of a simple sphere, the 
cell-membrane, are exhibited all the essential phenomena 
of life — growth, development, and reproduction. The 
physiology of these minute organisms is of peculiar inter¬ 
est, since all animal structure is but the multiplication of 
the cell as a unit, and the whole life of an animal is that 
of the cells which compose it: in them and by them all 
its vital processes are carried on. 14 

The structure of a cell can be seen in blood-corpuscles, 
by diluting with a weak (i per cent.) solution of salt a 
drop of blood from a Frog, and placing it under the mi¬ 
croscope. (See Fig. 63.) 

2. Tissues.—There are organisms of the lowest grade 
(as Gregarina) which consist of a single cell, living for and 
by itself. In this case, the animal and cell are identical: 
the Gregarina has as much individuality as the Elephant. 
But all animals, save these unicellular beings, are mainly 
aggregations of cells: for the various parts of a body are 
not only separable by the knife into bones, muscles, nerves, 
etc., but these are susceptible of a finer analysis by the 
microscope, which shows that they arise from the devel¬ 
opment and union of cells. These cellular fabrics, called 
tissues, differ from one another both chemically and struct¬ 
urally, but agree in being permeable to liquids — a prop¬ 
erty which secures the flexibility of the organs so essential 
to animal life. Every part of the human body, for exam- 



ORGANIZATION. 


33 


pie, is moist: even the hairs, nails, and cuticle contain 
water. The contents as well as the shape of the cells are 
usually modified according to the tissue which they form: 
thus, we find cells containing earthy matter, iron, fat, mu¬ 
cus, etc. 

In plants, the cell always retains the characters of the 
cell; but in animals (after the embryonic period) the cell 
usually undergoes such modifications that the cellular form 
disappears. The cells are connected together or enveloped 
by an intercellular substance (blastema), which may be 
watery, soft, and gelatinous, firmer and tenacious, still 
more solid and hyaline, or hard and opaque. In the fluids 
of the body, as the blood, the cells are separate; i. e ., the 
blastema is fluid. But in the solid tissues the cells coa¬ 
lesce, being simply connected, as in the epidermis, or united 
into fibres and tubes. 

In the lowest forms of life, and in all the higher ani¬ 
mals in their embryonic state, the cells of which they are 
composed are not transformed into differentiated tissues: 
definite tissues make their first appearance in the Sponges, 
and they differ from one another more and more widely 
as we ascend the scale of being. In other words, the bod¬ 
ies of the lower and the immature animals are more uni¬ 
form in composition than the higher or adult forms. In 
the Vertebrates only are all the following tissues found 
represented: 

(1) Epithelial Tissue.— This is the simplest form of cellu¬ 
lar structure. It covers all the free surfaces of the body, 
internal and external, so that an animal may be said to be 
contained between the walls of a double bag. That which 
is internal, lining the mouth, windpipe, lungs, blood-ves¬ 
sels, gullet, stomach, intestines—in fact, every cavity and 
canal — is called epithelium. It is a very‘delicate skin, 
formed of flat or cylindrical cells, and in some parts (as in 
the wind-pipe of air-breathing animals, and along the gills 

3 


34 


COMPARATIVE ZOOLOGY. 



of the Oyster) is covered with cilia, or minute hairs, about 
of an inch long, which are incessantly moving. Con¬ 
tinuous with this in ¬ 
ner lining of the 
body (as seen on the 
lip), and covering 
the outside, is the 
epidermis , or cuti¬ 
cle. It is the outer 
layer of the “skin,” 
which we can re- 

Fig. 2.—Various kinds of Epithelium Cells: a, colum- U10Ve by a blister, 
nar from small intestine; 3, a single cell, showing d in M ^ in 

nucleus; &, ciliated, from one of the small air- 

tubes; d, the same, from the windpipe, with single thickness from —1— 
cell magnified about 200 times; c, squamous, from . 8 0 

eyelid of a calf, showing changes of form, from the of an inch On the 
deep to superficial cells, 1 being the scurf. , 

cheek to T V on the 
sole of the foot. It is constantly wearing off at the sur¬ 
face, and as constantly growing in the deeper portion; and 
in the process of growth and passage outward, the cells 
change from the spherical form to dead horny scales (seen 
in scurf and dandruff). In the lower layer of the cuticle 
we find the pigment cells, characteristic of colored races. 
Neither the epidermis nor the corresponding tissue within 
(epithelium) has any blood-vessels or nerves. The epithe¬ 
lial tissue, then, is simply a superficial covering, bloodless 
and insensible, protecting the more delicate parts under¬ 
neath. Hairs, horns, hoofs, nails, claws, corns, beaks, scales, 
tortoise-shell, the wings of Insects, etc., are modifications 
of the epidermis. 

The next three sorts of tissue are characterized by a 
great development of the intercellular substance, while 
the cells themselves are very slightly modified. 

(2) Connective Tissue.— This is the most extensive tissue 
in animals, as it is the great connecting medium by which 
the different parts are held together. Could it be taken 




ORGANIZATION. 


35 


out entire, it would be a complete mould of all the organs. 
It surrounds the bones, muscles, blood-vessels, nerves, and 
glands, and is the substance 
of the ligaments, tendons, 

“true skin,” raucous mem¬ 
brane, ete. It varies in 
character, being soft, ten¬ 
der, and elastic, or dense, 
tough, and generally un¬ 
yielding. In the former 
state, it consists of innu¬ 
merable fine white and yel¬ 
low fibres, which interlace 

in all directions, leaving Fi«. 3.—Connective Tissue, showing areolar 
. . . . structure, X 25. 

irregular spaces, and form¬ 
ing a loose, spongy, moist web. In the latter, the fibres 




Fig. 4—Connective Tissue from human peritoneum; highly magnified; a , blood¬ 
vessel. 










36 


COMPARATIVE ZOOLOGY. 


are condensed into sheets or parallel cords, having a wavy, 
glistening appearance. Such structures are the fascise and 
tendons. Connective tissue is not very sensitive. It con¬ 
tains gelatine —the matter which tans when hide is made 
into leather. In this tissue the intercellular substances 
take the form of fibres. The white fibres are inelas¬ 
tic, and from 4 - 0 -to - g4 ow of an inch in diameter. 
They are best seen in the tendons. The yellow fibres are 
elastic, curled at the ends, very long, 
and from - zT^ in? to of an inch in 
diameter. They are shown in the 
hinge-ligament of an Oyster. Connec¬ 
tive tissue appears areolar, i. e ., shows 
interspaces, only under the microscope. 
(3) Cartilaginous Tissue. —This tissue, 



The space between the 
cells is filled with trans¬ 
parent intercellular sub- 


Fig. 5.—Hyaline Cartilage, 

Diagram: a, cartilage 
cell; 6, cell about to di¬ 
vide; c, cell divided iu to known also as “gristle, is composed 

two; d, into four parts. /• ii • i i i i • i . 

ot cells imbedded in a granular or hy¬ 
aline substance, which is dense, elastic, 
stance; highly magni- bluish white, and translucent. It is 

fled. 

found where strength, elasticity, and 
insensibility are wanted, ate at the 
joints. It also takes the place of the 
long bones in the embryo. When 
cartilage is mixed with connective tis¬ 
sue, as in the ear, it is called fibro-car- 
tilage. 

(4) Osseous Tissue. —This hard, opaque 
tissue, called “ bone,” differs from the 
former two in having the intercellular 
spaces or meshes filled with phosphate 
of lime and other earths, instead of a 
a hyaline or fibrous substance. It may 
be called petrified tissue—the quantity 



Fig. 6.—Ossifying Carti¬ 
lage, x 10 ; a, cartilage 


ceils, passing into com- 0 f earthy matter, and therefore the brit- 

pact bone, c, and then ^ 7 

spongy bone, e. tleness of the bone, increasing with the 







ORGANIZATION. 


37 




age of the animal. If a chicken-bone be left in dilute 
muriatic acid several days, it may be tied into a knot, since 
the acid has dissolved 
the lime, leaving noth¬ 
ing but cartilage and 
connective tissue. If a 
bone be burned, it be¬ 
comes light, porous, and 
brittle, the lime alone 


Bone is a very vas¬ 
cular tissue; that is, it 
is traversed by minute 

blood-vessels and nerves, ^ m „ 

7 Fig. 7.—Transverse section of a Bone (Human 
which pass through a Femur), x 50, showing Haversian canals. 

net-work of tubes, called Haversian canals. The canals 
average 1 - 0 1 6 0 - of an inch, being finest near the surface of 
the bone, and larger further in, where they form a cancel¬ 
lated or spongy structure, and finally merge (in the long 

bones) into the central 
cavity, containing the 
marrow. Under the 
microscope, each canal 
appears to be the cen¬ 
tre of a multitude of 
laminae , or plates, ar¬ 
ranged around it. Ly¬ 
ing between these plates 
are little cavities, called 
lacunae , from which ra¬ 
diate exceedingly fine 

Fig. S.—Frontal Bone of Human Skull under the P 01 es ? CCtndUculi . 

microscope, showing lacuni and canaliculi. These represent the 

original cells of the bone, and differ in shape and size in 


different animals. 




COMPARATIVE ZOOLOGY. 


True bone is found only in Vertebrates, or back-boned 
animals. 

(5) Dental Tissue.— Like bone, a tooth is a combination 
of earthy and animal matter. It may be called petrified 
skin. In the higher animals, it consists of three parts: 
dentine , forming the body of the tooth, and always pres¬ 
ent; enamel , capping the crown; and cement , covering the 
fangs (Fig. 31). The last is true bone, or osseous tissue. 



Fig. 9.—Highly magnified section of Dentine and Cement, from the fang of a Human 
Molar: a, 6, marks of the original dentinal pulp; d, dentinal tubes, terminating 
in the very sensitive, modified layer, g; h, cement. 

Dentine resembles bone, but differs in having neither la¬ 
cunae nor (save in Shark’s teeth) canaliculi. It shows, in 
place of the former, innumerable parallel tubes, reaching 
from the outside to the pulp-cavity within. The “ ivory ” 
of Elephants consists of dentine. Enamel is the hardest 
substance in the body, and is composed of minute six-sided 
fibres, set closely together. It is want¬ 
ing in the teeth of most Fishes, Snakes, 
Sloths, Armadillos, Sperm-whales, etc. 

True dental tissue is confined to 
Vertebrates. 

(6) Adipose Tissne.— Certain cells be¬ 
come greatly enlarged and filled with 
fat, so that the original protoplasm oc¬ 
cupies a very small part of the space 
within the cell-membrane. These cells 
are united into masses by connective 
tissue, in the skin (as in the “blub- 



Fig. 10.—Adipose Tissue, a ; 
•with fibres of connective 
tissne, b. 










ORGANIZATION. 


39 


ber” of whales), between the muscles (as in “streaky” 
meat), or in the abdominal cavity, in the omentum, mes¬ 
entery, or about the kidneys. The marrow of bones is an 
example. Globules of fat occur in many Molluscs and 
Insects; but true adipose tissue is found only in back¬ 
boned animals, particularly the herbivorous. In the aver¬ 
age Man, it constitutes about part of his weight, and a 
single Whale has yielded 120 tons of oil. The fat of 
animals has the different names of oil, lard, tallow, suet, 
spermaceti, etc. It is a reserve of nutriment in excess of 
consumption, serving also as a packing material, and as 
a protection against cold. 

(7) Muscular Tissue.— If we examine a piece of lean meat, 
we find it is made up of a number of fasciculi, or bundles 
of fibres, placed side by 
side, and bound together 
by connective tissue. The 
microscope informs us 
that each fibre is itself a 
bundle of smaller fibres; 
and when one of these is 
more closely examined, 
it is found to be enclosed 
in a delicate, glossy tube, 
called the sarcolemma. 

This tube is filled with 
very minute, parallel 
fibrils, averaging 
of an inch in diameter, and having a striated aspect. 
Tissue of this description constitutes all ordinary muscle, 
or “ lean meat,” and is marked by regular cross-lines, or 
strice. 

Besides this striated muscular tissue, there exist, in the 
coats of the stomach, intestines, blood-vessels, and some oth¬ 
er parts of Vertebrates, smooth muscular fibres, or mem- 



Fig. 11.— Striated Muscular Fibre (of the Pig), 
X 200. The constituent fibres are seen at a; 
c is a fasciculus, or bundle. 




COMPARATIVE ZOOLOGY. 


*40 

branes, which show a nucleus under the microscope, and 
do not break up into fibrils (Fig. 122). The gizzards of 
fowls exhibit this form. 

All muscle has the property of shorten¬ 
ing itself when excited ; but the contraction 
of the striated kind is under the control of 
the will, while the movement of the smooth 
fibres is involuntary. 18 Muscles are well sup¬ 
plied with arteries, veins, and nerves; but 
the color is due to a peculiar pigment, not 
to the blood. 

Muscular tissue is found in all animals 
from the Coral to Man. 

(8) Nervous Tissue. —Nervous matter exists 
under three forms: First—the cellular , con¬ 
sisting: of nucleated cells, varying from e oVu 

Fig. 12.—Striated & .. 

Muscular Fibres, to of an inch in diameter, and found in 
Man, divided by the nerve-centres (fig. 132), the gray por- 
?Z S r p ar e »te e S“ tion of the brain, spinal cord, and other gan- 
cieated portions. gfi a . Second—th q fibrous, consisting of pale, 
flat, extremely fine filaments. They abound in the sympa¬ 
thetic nerves, and are the only nerves found in the Inverte¬ 
brates. Third—the tubular. These are much 
larger than the fibrous, the coarsest being 
-reVo of an inch in diameter. They consist 
of tubes enclosing a transparent fibre and a 
fatty substance called the nerve-marrow. 17 
The delicate tube itself is called neurilem¬ 
ma, analogous to the sarcolemma of mus- FrG ; 13 -- structnre 
cular tissue. Nerve-tubes are found only 
in back-boned animals, in the white sub¬ 
stance of the brain, spinal cord, and in the 
nerves. 

A bundle of fibrous or tubular nervous matter, snr 
rounded by connective tissue, constitutes a nerve. 


sheath, or neuri¬ 
lemma; 2, med¬ 
ullary substance 
of Schwann; 3, 
axis cylinder, or 
primitive band. 









ORGANIZATION. 


41 



Fig. 14.—A Ganglion of the Sympathetic Nerve of a Mouse. 

3. Organs, and their Functions.—Animals, like Plants, 
grow, feel, and move; these three are the capital facts of 
every organism. Besides these there may be some pecul¬ 
iar phenomena, as motion and will. 

Life is manifested in certain special operations, called 
functions , performed by certain special parts, called or¬ 
gans. Thus, the stomach is an organ, whose function is 
digestion. A single organ may manifest vitality, but it 
does not (save in the very lowest forms) show forth the 
whole life of the animal. For, in being set apart for a 
special purpose, an organ takes upon itself, so to speak, to 
do something for the benefit of the whole animal, in return 
for which it is absolved from doing many things. The 
stomach is not called upon to circulate or purify the blood. 

There may be functions without special organs, as the 
Amoeba digests, respires, moves, and reproduces by its 
general mass. But, as we ascend the scale of animal life, 
we pass from the simple to the complex: groups of cells 
or tissues, instead of being repetitions of each other, take 
on a difference, and become distinguished as special parts 
with specific duties. The higher the rank of the animal, 
the more complicated the organs. The more complicated 
the structure, the more complicated the functions. But in 





42 


COMPARATIVE ZOOLOGY. 


all animals, the functions are performed under conditions 
essentially the same. Thus, respiration in the Sponge, the 
Fish, and in Man has one object and one means, though 
the methods differ. A function, therefore, is a group of 
similar phenomena effected by analogous structures. 

The life of an animal consists in the accumulation and 
expenditure of force. The tissues are storehouses of 
power, which, as they waste, is given off in various forms. 
Thus, the nervous tissue generates nerve-force; the mus¬ 
cles, motion. If we contemplate the phenomena presented 
by a Dog, the most obvious fact is his power of moving 
from place to place, a power produced by the interplay of 
muscles and bones. We observe, also, that his motions 
are neither mechanical nor irregular; there is method in 
his movement. He has the power of willing, seeing, hear¬ 
ing, feeling, etc.; and these functions are accomplished by 
a delicate apparatus of nerves. 

But the Dog does not exhibit perpetual motion. Sooner 
or later he becomes exhausted, and rest is necessary. Sleep 
gives only temporary relief. In every exercise of the 
muscles and nerves there is a consumption or w T aste of 
their substance. The blood restores the organs, but in 
time the blood itself needs renewal. If not renewed, the 
animal becomes emaciated, for the whole body is laid un¬ 
der contribution to furnish a supply. Hence the feelings 
of hunger and thirst, impelling the creature to seek food. 
Only this will maintain the balance between waste and 
repair. We notice, therefore, an entirely different set of 
functions, involving, however, the use of motion and will. 
The Dog seizes a piece of meat, grinds it between its 
teeth, sends it into the stomach, where it is digested, and 
then into the intestine, where it is further changed; there 
the nourishing part is absorbed, and carried to the heart, 
which propels it through tubes, called blood-vessels, all 
over the body. In this process of digestion, certain fluids 


ORGANIZATION. 


43 


are required, as saliva, gastric juice, and bile: these are 
secreted by special organs, called glands. Moreover, since 
not all the food eaten is fitted to make blood, and as the 
blood itself, in going around the body, acts like a scaven¬ 
ger, picking up worn-out particles, we have another func¬ 
tion, that of excretion, or removal of useless matter from 
the system. The kidneys and lungs do much of this; but 
the lungs do something else. They expose the blood to 
the air, and introduce oxygen, which, we shall find, is 
essential to the life of every animal. 

These centripetal and centrifugal movements in the 
body—throwing in and throwing out—are so related and 
involved, especially in the lower forms, that they cannot 
be sharply defined and classified. It has been said that 
every Dog has two lives — a vegetative and an animal. 
The former includes the processes of digestion, circulation, 
respiration, secretion, etc., which are common to all life; 
the functions of the other, as motion, sensation, and will, 
are peculiar to animals. The heart is the centre of the 
vegetative life, and the brain is the centre of the animal 
life. The aim of the vegetative organs is to nourish the 
individual, and reproduce its kind; the organs of locomo¬ 
tion and sense establish relations between the individual 
and the w T orld without. The former maintain life; the 
others express it. The former develop, and afterwards 
sustain, the latter. The vegetative organs, however, are 
not independent of the animal; for without muscles and 
nerves we could not procure, masticate, and digest food. 
The closer the connection and dependence between these 
two sets of organs, the higher the rank. 18 

All the apparatus and phenomena of life may be in¬ 
cluded under the heads of 

Nutrition, 

Motion, 

Sensation. 


44 


COMPARATIVE ZOOLOGY. 


These three are possessed by all animals, but in a vari¬ 
ety of ways. No two species have exactly the same mech¬ 
anism and method of life. We must learn to distinguish 
between what is vital and what is only accessory. That 
only is essential to life which is common to all forms of 
life. Our brains, stomachs, livers, hands, and feet are 
luxuries. They are necessary to make us human, but not 
living, beings. Half of our body is taken up with a com¬ 
plicated system of digestion; but the Amoeba has neither 
mouth nor stomach. We have an elaborate apparatus of 
motion; the Oyster cannot stir an inch. 

Nutrition , Motion , and Sensation indicate three steps 
up the grade of life. Thus, the first is the prominent 
function in the Coral, which simply “ vegetates, 1 ” the pow¬ 
ers of moving and feeling being very feeble. In the 
higher Insect, as the Bee, there is great activity with sim¬ 
ple organs of nutrition. In the still higher Mammal, as 
Man, there is less power of locomotion, though the most 
perfect nutritive system; but both functions are subordi¬ 
nate to sensation, which is the crowning development. 

In studying the comparative anatomy and physiology 
of the animal kingdom, our plan will be to trace the vari¬ 
ous organs and functions, from their simplest expression 
upward to the highest complexity. Thus Nutrition will 
begin with absorption, which is the simplest method of 
taking food; going higher, we find digestion, but in no 
particular spot in the body; next, we see it confined to a 
tube; then to a tube with a sac, or stomach; and, finally, 
we reach the complex arrangement of the higher animals. 


NUTRITION. 


45 


CHAPTER VI. 

NUTRITION. 

Nutrition is the earliest and most constant of vital op¬ 
erations. So prominent is the nutritive apparatus, that 
an animal has been likened to a moving sac, organized to 
convert foreign matter into its own likeness, to which the 
complex organs of animal life are but auxiliaries. Thus, 
the bones and muscles are levers and cords to carry the 
body about, while the nervous system directs its motions, 
in quest of food. 

The objects of nutrition are growth, repair, and propa¬ 
gation. The first object of life is to grow, for no animal 
is born finished. Some animals, like plants, grow as long 
as they live ; 19 but the majority soon attain a fixed size. 
In all animals, however, without exception, food is wanted 
for another purpose than growth, namely, to repair the 
waste which is constantly going on. For every exercise 
of the muscles and nerves involves the death and decay 
of those tissues, as shown by the excretions. The amount 
of matter expelled from the body, and the amount of nour¬ 
ishment needed to make good the loss, increase with the 
activity of the animal. The supply must equal the de¬ 
mand, in order to maintain the life of the individual; and 
as an organism can make nothing, it must seek it from 
without. Not only the muscles and nerves are wasted by 
use, but every organ in the body; so that the whole struct¬ 
ure needs constant renewal. An animal begins to die the 
moment it begins to live. The function of nutrition, 
therefore, is constructive , while motion and sensation are 
destructive . 


46 


COMPARATIVE ZOOLOGY. 


Another source of demand for food is the production of 
germs, to propagate the race, and the nourishment of such 
offspring in the egg and infantile state. This reproduc¬ 
tion and development of parts which can maintain an in¬ 
dependent existence is a vegetative phenomenon (for plants 
have it), and is a part of the general process of Nutrition. 
But it will be more convenient to consider it hereafter 
(chapters xix., xx.). Still another necessity for aliment 
among the higher animals is the maintenance of bodily 
heat. This will be treated under the head of Respiration. 

For the present, we will study Nutrition, as manifested 
in maintaining the life of an adult individual. 

In all animals, this process essentially consists in the in¬ 
troduction of food, its conversion into tissue , its oxidation , 
and the removal of worn-out material . 

1. The food must be procured, and swallowed. (Inges¬ 
tion.) 

2. The food must be dissolved, and the nutritious parts 
separated into a fluid. (Digestion.) 

3. The nutritive fluid must be carefully taken up, and 
then distributed all over the body. (Absorption and Cir¬ 
culation.) 

4. The tissues must repair their parts wasted by use, 
by transforming particles of blood into living matter like 
themselves. (Assimilation.) 

5. Certain matters must be strained from the blood, 
some to serve a purpose, others to be cast out of the sys¬ 
tem. (Secretion and Excretion.) 

6. In order to produce work and heat, the food must be 
oxidized, either in the blood or in the tissues, after assimi¬ 
lation. The necessary oxygen is obtained through expos¬ 
ure of the blood to the air in the lungs. (Respiration in 
part.) 

7. The waste products of this oxidation taken up by 
the blood must be got rid of; some from the lungs (car- 


THE FOOD OF ANIMALS. 47 

bon dioxide, water), some from the kidneys (water, urea, 
mainly), some from the skin (water, salines). (Inspira¬ 
tion in part, Excretion.) 

The mechanism to accomplish all this in the lowest 
forms of life is exceedingly simple, a single cavity and 
surface performing all the functions. But in the major¬ 
ity of animals the apparatus is very complicated: there is 
a set of organs for the prehension of food; another, for 
digestion; a third, for absorption; a fourth, for distribu¬ 
tion ; and a fifth, for purification. 


CHAPTER VII. 

THE FOOD OF ANIMALS. 

The term food includes all substances which contribute 
to nutrition, whether they simply assist in the process, or 
are actually appropriated, and become tissue. With the 
food is usually combined more or less indigestible matter, 
which is separated in digestion. 

Food is derived from the mineral, vegetable, and animal 
kingdoms. Water and salt, for example, are inorganic. 
The former is the most abundant, and a very essential 
article of food. Most of the lower forms of aquatic life 
seem to live by drinking: their real nourishment, how¬ 
ever, is present in the water in the state of solution. The 
Earthworm, some Beetles, and certain savage tribes of 
Men swallow earth; but this, likewise, is for the organic 
matter which the earth contains. As no animal is pro¬ 
duced immediately from inorganic matter, so no animal 
can be sustained by it. 

Nutritious or tissue-forming food comes from the or¬ 
ganic world, and is albuminous , as the lean meat of ani- 



48 


COMPARATIVE ZOOLOGY. 


mals and the gluten of wheat; oleaginous , as animal fat 
and vegetable oil; or saccharine , as starch and sugar. The 
first is the essential food-stuff; no substance can serve 
permanently for food—that is, can permanently prevent 
loss of weight in the body—unless it contains albuminous 
matter. As stated before, all the living tissues are albu¬ 
minous, and therefore albuminous food is required to sup¬ 
ply their waste. Albumen contains nitrogen, which is 
necessary to the formation of tissue; fats and sugars are 
rich in carbon, and therefore serve to maintain the heat 
of the body, and to repair part of the waste of tissues. 
Warm-blooded animals feed largely on farinaceous or 
starchy substances, which in digestion are converted into 
sugar. But any animal, of the higher orders certainly, 
whether herbivorous or carnivorous, would starve, if fed 
on pure albumen, oil, or sugar. Nature insists upon a 
mixed diet; and so we find in all the staple articles of 
food, as milk, meat, and bread, at least two of these prin¬ 
ciples present. As a rule, the nutritive principles in veg¬ 
etables are less abundant than in animal food, and the 
indigestible residue is consequently greater. The nutri¬ 
ment in fiesh increases as we ascend the animal scale; 
thus, Oysters are less nourishing than Fish; Fish, less than 
Fowl; and Fowl, less than the flesh of Quadrupeds. 

Many animals, as most Insects and Mammals, live solely 
on vegetable food, and some species are restricted to par¬ 
ticular plants, as the Silk-worm to the white mulberry. 
But the majority of animals feed on one another; such 
are hosts of the microscopic forms, and nearly all the ra¬ 
diated species, marine Mollusks, Crustaceans, Beetles, Flies, 
Spiders, Fishes, Amphibians, Beptiles, Birds, and clawed 
Quadrupeds. 

A few, as Man himself, are omnivorous, i. e ., are main¬ 
tained on a mixture of animal and vegetable food. The 
use of fire in the preparation of food is peculiar to Man, 


HOW ANIMALS EAT. 


49 


who has been called “ the cooking animal.” A few of the 
strictly herbivorous and carnivorous animals have shown 
a capacity for changing their diet. Thus, the Hoise and 
Cow may be brought to eat fish and flesh; the Sea-birds 
can be habituated to grain; Cats are fond of alligator- 
pears ; and Dogs take naturally to the plantain. Certain 
animals, in passing from the young to the mature state, 
make a remarkable change of food. Thus, the Tadpole 
feeds upon vegetable matter; but when it becomes a Frog 
it lives on Insects. 

Many tribes, especially of Reptiles and Insects, are able 
to go without food for months, or even years. Insects in 
the larval, or caterpillar, state are very voracious; but 
upon reaching the perfect, or winged, state, they eat little 
—some species taking no food at all, the mouth being act¬ 
ually closed. The males of some Rotifers and other tribes 
take no food from the time of leaving the egg until death. 

In general, the greater the facility with which an animal 
obtains its food, the more dependent is it upon a constant 
supply. Thus, carnivores endure abstinence better than 
herbivores, and wild animals than domesticated ones. 


CHAPTER VIII. 

HOW ANIMALS EAT. 

1. The Prehension of Food.— (1) Liquids.—The sim¬ 
plest method of taking nourishment is by absorption 
through the skin. The Tape-worm, for example, has 
neither mouth nor stomach, but imbibes the digested food 
of the animal it infests. Many other animals, especially 
Insects, live upon liquid food, but obtain it by suction 
through a special orifice or tube. Thus, we find a mouth, 

4 



50 


COMPARATIVE ZOOLOGY. 


or sucker, furnished with teetli for lancing the skin of an¬ 
imals, as in the Leech; a bristle-like tube fitted for pierc¬ 
ing, as in the Mosquito; a sharp sucker armed with barbs, 
to fix it securely during the act of sucking, as in the 
Louse; and a long, flexible proboscis, as in the Butterfly. 
Bees have a hairy, channelled tongue, and Flies have one 
terminating in a large fleshy knob, with or without little 
“ knives ” at the base for cutting the skin: both lap, rather 
than suck, their food. 

Most animals drink by suction, as the Ox; and a few 
by lapping, as the Dog; the Elephant pumps the water 
up with its trunk, and then pours it into its throat; and 
Birds (excepting Doves) fill the beak, and then, raising 
the head, allow the water to run down. 

Many aquatic animals, whose food consists of small par¬ 
ticles diffused through the water, have an apparatus for 
creating currents, so as to bring such particles within their 
reach. This is particularly true of low, fixed forms, which 
are unable to go in search of their food. Thus, the Sponge 
draws nourishment from the water, which is made to cir¬ 
culate through the system of canals traversing its body 
by the vibration of minute hairs, or cilia, lining parts of 
the canals (Fig. 189). The microscopic Infusoria have 
cilia surrounding the mouth, with which they draw or 
drive into the body little currents containing nutritious 
particles. Bivalve mollusks, as the Oyster and Clam, are 
likewise dependent upon this method of procuring food, 
the gills being fringed with cilia. So the singular fish, 
Amphioxus (the only example among Vertebrates), em¬ 
ploys ciliary action to obtain the minute organisms on 
which it feeds. The Greenland Whale has a mode of in¬ 
gestion somewhat unique, gulping great volumes of water 
into its mouth, and then straining out, through its whale¬ 
bone sieve, the small animals which the water may con¬ 
tain (Fig. 343). 


HOW ANIMALS EAT. 


51 


(2) Solids. —When the food is in solid masses, whether 
floating in water or not, the animal is usually provided 
with prehensile appendages for v 

taking hold of it. The jelly- 
like Amoeba has neither mouth 



nor stomach, but extemporizes 
them, seizing its food by means 
of its soft body. The food then 
passes through the outer wall 
into the softer interior, where it 


Fig. 15.—A Rhizopod ( RotaliaVeneta ), 


is digested. The waste particles with pseudopodia extended, X 30. 
are passed out in a similar way. In the Foraminifers, 
thread-like projections of the body are thrown out (pseu¬ 
dopodia) which adhere to the prey. The soft jelly-like 
substance of the body then flows down the pseudopodium, 
collects about the food, and digests it (Fig. 15). 

A higher type is seen in Polyps and Jelly-fishes, which 
have hollow tentacles around the entrance to the stomach 
(Fig. 193). These tentacles are contractile, and, moreover, 
are covered with an immense number of minute sacs, in 
which a highly elastic filament is coiled up spirally (lasso- 
cells, nettle-cells). When the tentacles are touched by a 
passing animal, they seize it, and at the same moment 
throw out their myriad filaments, like so many lassos, 
which penetrate the skin of the victim, and probably also 
emit a fluid, which paralyzes it; the mouth, meanwhile, 
expands to an extraordinary size, and the creature is soon 
engulfed in the digestive bag. 

In the next stage, we find no tentacles, but the food is 
brought to the mouth by the flexible lobes of the body, 
commonly called “arms,” which are covered with hun¬ 
dreds of minute suckers; and if the prey, as an Oyster, is 
too large to be swallowed, the stomach protrudes, like a 
proboscis, and sucks it out of its shell. This is seen in 
the Star-fish (Fig. 126). 


52 


COMPARATIVE ZOOLOGY. 


A great advance is shown by the Sea-urchin, whose 
mouth is provided with five sharp teeth, set in as many 
jaws, and capable of being projected so as to grasp, as w T ell 
as to masticate, its food (Figs. 214, 28). 

In Mollusks having a single shell, as the Snail, the chief 
organ of prehension is a strap-like tongue, covered with 
minute recurved teeth, or spines, with which the animal 
rasps its food, while the upper lip 
is armed with a sharp, horny 
plate (Fig. 29). In many marine 
species, as the Whelk, the tongue 
is situated at the end of a retrac¬ 
tile proboscis, or muscular tube. 
In the Cuttle-fish, we see the sud¬ 
den development of an elaborate 
system of prehensile organs. Be¬ 
sides a spinous tongue, it has a 
pair of hard mandibles, resem¬ 
bling the beak of a Parrot, and 
working vertically; and around 
the mouth are eight or ten pow- 
’1“: erful arms furnished with numer- 

the arm, containing nerve and ar- 0 US CUD-like SUCkerS. So perfect is 

tery; c, cellular tissue; d, radiat- * t 

ing fibres; h, raised margin of the adhesion of these suckers, that 

the disk around the aperture/, g, ... . . 

which contains a retractile mem- it is easier to tear away a limb 

brane, or “piston," u than ft from its hold. 

The Earth-worm swallows earthy 
matter and decaying leaves, which 
it secures with its lips, the up¬ 
per one being prolonged. Other 
worms (as Nereis) are so construct¬ 
ed that the gullet, which is fre¬ 
quently armed with teeth and for¬ 
ceps, Can be turned inside out, to Fig.it.—N ereis — head, with ex- 
form a proboscis for seizing prey. y ' 





HOW ANIMALS EAT. 


53 


The Arthropoda exhibit a great variety of means for 
procuring nourishment, in addition to the suctorial com 
trivances already mentioned, the innumerable modifica¬ 
tions of the mouth corresponding to the diversity of food. 
Millepedes, Caterpillars, and Grubs have a pair of horny 
jaws moving horizontally. The Centipede has a second 
pair of jaws, which are really modified feet, terminated 
by curved fangs containing a poison-duct. The Horse¬ 
shoe Crab uses its feet for prehension, and the thighs, or 
basal joints, of its legs to masticate the food and force it 
into the stomach. The first six pair of legs in the Lob¬ 
ster and Crab are likewise appropriated to conveying food 
into the mouth, the sixth being enormously developed, 
and furnished with powerful 
pincers. Scorpions have a 
similar pair of claws for pre¬ 
hension, and also a pair of 
small forceps for holding 
the food in contact with the 
mouth. In their relatives, Fig. IS.—One of the Fangs, or Perforated 
the Spiders, the claws are Mandibles, of the s P ide, 

wanting, and the forceps end in a fang, or hook, which is 
perforated to convey venom. 20 

The biting Insects, as Beetles and Locusts, have two 
pairs of horny jaws, which open sidewise, one above and 
the other below the oral orifice. The upper pair are called 
mandibles; the lower, maxillae. The former are armed 
with sharp teeth, or with cutting edges, and sometimes 
are fitted, like the molars of quadrupeds, to grind the 
food. The maxillae are usually composed of several parts, 
some of which serve to hold the food, or to help in divid¬ 
ing it, while others (palpi) are sensory. There is generally 
present a third pair of jaws —the labium — which are 
united in the middle line, and serve as a lower lip. They 
also bear palpi. The Mantis seizes its prey with its long 



54 


COMPARATIVE ZOOLOGY. 


fore-legs, crushes it between its thighs, which are armed 
with spines, and then delivers it up to the jaws for masti¬ 
cation. All Arthropods move their jaws horizontally. 

The back-boned animals generally apprehend food by 
means of their jaws, of which there are two, moving ver¬ 
tically. The toothless Sturgeon draws in its prey by pow¬ 
erful suction. The Hag-fish has a single tooth, which it 
plunges into the sides of its victim, and, thus securing a 
firm hold, bores its way into the flesh by means of its saw¬ 
like tongue. But Fishes are usually well provided with 
teeth, which, being sharp and curving inward, are strictly 
prehensile. The fins and tongue are not prehensile. A 
mouth with horny jaws, as in the Turtles, or bristling with 
teeth, as in the Crocodile, is the only means possessed by 
nearly all Amphibians and Reptiles for securing food. 
The Toad, Frog, and Chameleon capture insects by dart ¬ 
ing out the tongue, which is tipped with glutinous saliva. 
The constricting serpents (Boas) crush their prey in their 
coils before swallowing; and the venomous Snakes have 
a poison-fang. No reptile has prehensile lips. All Birds 
use their toothless beaks in procuring food, but birds of 
prey also seize with their talons, and Woodpeckers, Hum¬ 
mers, and Parrots with their tongues. The beak varies 
greatly in shape, being a hook in the Eagle, a probe in the 
Woodpecker, and a shovel in the Duck. 

Among the Quadrupeds we find a few special contriv¬ 
ances, as the trunk of the Elephant, and the long tongues 
of the Giraffe and Ant-eater; but, as a rule, the teeth are 
the chief organs of prehension, always aided more or less 
by the lips. Ruminants, like the Ox, having hoofs on 
their feet, and no upper front teeth, employ the lips and 
tongue. Such as can stand erect on the hind-legs, as the 
Squirrel, Bear, and Kangaroo, use the front limbs for hold¬ 
ing the food and bringing it to the mouth, but never one 
limb alone. The clawed animals, like the Cat and Lion, 


HOW ANIMALS EAT. 


55 


make use of their feet in securing prey, all four limbs be¬ 
ing furnished with curved retractile claws; but the food 
is conveyed into the mouth by 
the movement of the head and 
jaws. Man and the Monkeys em¬ 
ploy the hand in bringing food 
to the mouth, and the lips and 
tongue in taking it into the cavi¬ 
ty. The thumb on the human 
hand is longer and more perfect 
than that of the Apes and Mon¬ 
keys; but the foot of the latter 
is also prehensile. 

2. The Mouths of Animals. 

—In the Parasites, as the Tape¬ 
worm, which absorb nourishment 
through the skin, and Insects, as 
the May-fly and Bot-fly, wdiich do Fig. 19 .-Arm of the Thumbless 
all their eating in the larval state, Monkey (Ateies). 

the mouth is either wanting or rudimentary. The Amoeba, 
also,’ has no mouth proper, its food passing through the 
firmer outside part of the bit of protoplasm which consti¬ 
tutes its body. Mouth and anus are thus extemporized, 
the opening closing as soon as the food or excrement has 
passed through. 

In the Infusoria the mouth is a round or oval opening 
leading through the cuticle and outer layer of protoplasm 
to the interior of the single cell which makes their body. 
It is usually bordered with cilia, and situated on the side 
or at one end of the animal. 

An elliptical or quadrangular orifice, surrounded with 
tentacles, and leading directly to the stomach, is the ordi¬ 
nary mouth of the Polyps and Jelly-fishes. In those 
which are fixed, as the Actinia, Coral, and Hydra, the 
mouth looks upward: in those which freely move about, 



56 


COMPARATIVE ZOOLOGY. 


as the Jelly-fish, it is generally underneath, the position of 
the animal being reversed. In some, the margin, or lip, 
is protruded like a proboscis; and in all it is exceedingly 
dilatable. 

The mouth of the Star-fish and Sea-urchin is a simple 
round aperture, followed by a very short throat. In the 
Star-fish, it is enclosed by a ring of hard tubercles and a 
membrane. In the Sea-urchin, it is surrounded by a mus¬ 
cular membrane and minute tentacles, and is armed with 
five sharp teeth, set in as many jaws, resembling little 
conical wedges (Fig. 28). 

Among the headless Mollusks, the oral apparatus is very 
simple, being inferior to that of some of the radiated ani¬ 
mals. In the Oyster and Bivalves generally, the mouth 
is an unarmed slit—a mere inlet to the oesophagus, situ¬ 
ated in a kind of hood formed by the union of the gills 
at their origin, and between two pairs of delicate lips. 
These lips make a furrow, along which pass the particles 
of food drawn in by the cilia. 

Of the higher Mollusks, the little Clio (one of the Ptero- 
pods) has a triangular mouth, with two jaws armed with 
sharp horny teeth, and a tongue covered with spiny book¬ 
lets all directed backward. Some Univalves have a sim¬ 
ple fleshy tube. Others, as the Whelk, have an extensible 
proboscis, which unfolds itself, like the finger of a glove, 
and carries within it a rasp-like tongue, which can bore 


into the hardest shells. Such 
as feed on vegetable matter, 
as the Snail, have no probos¬ 
cis, but on the roof of the 



Fig. 20 .—Jaw of the Common Snail mouth a Curved horny plate 


(Helix albolabris). 


fitted to cut leaves, etc., which 


are pressed against it by the lips, and on the floor of the 
mouth a small tongue covered with delicate teeth. As fast 
as the tongue is worn off by use, it grows out from the root. 


HOW ANIMALS EAT. 


57 


The mouth of the Cuttle-fish is the most elevated type 
below that of the Fishes. A broad circular lip nearly 
conceals a pair of strong horny mandibles, not unlike the 
beak of a parrot, but reversed, the upper mandible being 
the shorter of the two, and the jaws, which are cartilagi¬ 
nous, are imbedded in a mass of muscles, and move ver¬ 
tically. Between them is a fleshy tongue covered with 
teeth. 

The parasitic Worms, living within or on the outside 
of other animals, generally have a sucker at one end or 
underneath, serving simply for attachment, and another 
which is perforated. The latter is a true suctorial mouth, 
being the sole inlet of food. It is often surrounded with 
booklets or teeth, which serve both to scarify the victim 
and secure a firm hold. In the Leech, the mouth is a 
triangular opening with thick lips, the upper one pro¬ 
longed, and with three jaws. In many Worms it is a 
fleshy tube, which can be drawn in or extended, like the 
eye-stalks of the Snail, and contains a dental apparatus 
inside (Fig. 17). 

Millepedes and Centipedes have two lateral jaws and a 
four-lobed lip. 

In Lobsters and Crabs the mouth is situated underneath 
the head, and consists of a soft upper lip, then a pair of 
upper jaws provided with a short feeler, below which is a 
thin bifid lower lip ; then follow two pairs of membranous 
under jaws, which are lobed and hairy; and next, three 
pairs of foot-jaws (Fig. 250). The Horse-shoe Crab has 
no special jaws, the thighs answering the purpose. The 
Barnacle has a prominent mouth, with three pairs of rudi¬ 
mentary jaws. 

With few exceptions, the mouths of Insects in the lar¬ 
val state are fitted only for biting, the two jaws being 
horny shears. But in the winged, or perfect, state, Insects 
may be divided into the masticating (as the Beetle) and 


58 


COMPARATIVE ZOOLOGY. 



Fig. 21.—Mouth of a Locust dissected: 1, labrum, or upper lip; 2, mandibles; 3, 
jaws; 4, labium, or lower lip; 5, tongue. The appendages to the maxillae and 
lower lip are palpi. 


the suctorial (as the Butterfly). In the former group, the 
oral apparatus consists of two pairs of horny jaws (mandi¬ 
bles and maxillce ), which work horizontally between an 
upper ( labrum ) and an under (labium) lip. The maxillae 
and under lip carry sensitive jointed feelers (palpi). The 
front edge of the labium is commonly known as the tongue 
( ligula ). 21 In such a mouth, the mandibles are the most 
important parts; but in passing to the suctorial Insects, 
we find that the mandibles are secondary to the maxillae 
and labium, which are the only means of taking food. In 



HOW ANIMALS EAT. 


59 


the Bee tribe, we have a transi¬ 
tion between the biting and the 
sucking Insects—the mandibles 
“supply the place of trowels, 
spades, pickaxes, saws, scissors, 
and knives,” while the maxillae 
are developed into a sheath to 
enclose the long, slender, hairy 
tongue which laps up the sweets 
of flowers. In the suctorial But¬ 
terfly, the lips, mandibles, and 
palpi are reduced to rudiments, 
while the maxillae are the only 
useful oral organs. These are 
excessively lengthened into a 
proboscis, their edges locking 
by means of minute teeth, so as 
to form a central canal, through 
which the liquid food is pumped 
up into the mouth. Seen un¬ 
der the microscope, the proboscis is made up of innumer¬ 
able rings interlaced with spiral muscular fibres. The 

proboscis of the Fly 
is a modified lower 
lip; that of the Bugs 
and Mosquitos, fitted 
both for piercing and 
suction, is formed by 
the union of four 
bristles, which are 
the mandibles and 
maxilla3 strangely al¬ 
tered, and encased in 
the labium when not 

Fig. 23.—Proboscis of a Butterfly. in USe. 




Flo. 22.— Head of a Wild Bee (An- 
thophora retusa), front view: a, 
compound eyes; b , clypeus; c, 
three simple eyes; d, antennae; e, 
labrum ; /, mandibles; i, maxillae; 
h, maxillary palpi'; l , palpifer; j, 
labial palpi; m, paraglossae; k t 
ligula. 




60 


COMPARATIVE ZOOLOGY. 



Fro. 24.—Mouth of the 
Horse-fly (Tabanus lin- 
eola): a, antennae; m, 
mandibles; mx, max- 


As most of the Arachnids live by suc¬ 
tion, the jaws are seldom used for masti¬ 
cation. In the Scorpion, the apparent 
representatives of the mandibles of an 
Insect are transformed into a pair of 
small forceps, and the palpi, so small in 
Insects, are developed into formidable 
claws: both of these organs are prehen¬ 
sile. In Spiders, the so-called mandi- 
iiise; mp, maxillary bles, which move more or less vertically, 

palpi; lb, labrum; l, , . 

labium, or tongue. end in a tang; and the club-like palpi, 
often resembling legs, have 
nothing to do with inges¬ 
tion or locomotion. Both 
Scorpions and Spiders have 
a soft upper lip, and a 
groove within the mouth, 
which serves as a canal 
while sucking their prey. 

The tongue is external, and 
situated between a pair of 
diminutive maxillae. 

In the Ascidians the first 
part of the alimentary canal 
is enormously enlarged and 
modified to serve as a gill- 
sac. At the bottom of this 
sac, and far removed from 
its external opening, lies 
the entrance to the diges- 
tive tract proper. Into it 

the particles of food enter- Fra .*.-under surtaceofMaie SpMer: 
ing with the water are con- poison-fang ; &, teeth on intei •ior mar- 
v gin of mandible > e »* A labium; g, thorax • 

veyed (y lg. Zi&j. h, limbs; i, abdomen; l, spinnerets; m, 

The mouth of Verte- JSSt ’*’ 7 pa ' p,18: d ’ dilated ter “ inal 





HOW ANIMALS EAT. 


61 


brates is a cavity with a fixed roof (the hard palate) and 
a movable floor (the tongue and lower jaw), having a trans¬ 
verse opening in front, 22 and a narrow outlet behind, lead¬ 
ing to the gullet. Save in Birds and some others, the 
cavity is closed in front with lips, and the margins of the 
jaws are set with teeth. 

In Fishes the mouth is the common entry to both the 
digestive and respiratory organs; it is, therefore, large, 
and complicated by a mechanism for regulating the tran¬ 
sit of the food to the stomach and the aerated w r ater to the 
gills. The slits leading to the gills are provided with 
rows of processes which, like a sieve, prevent the entrance 
of food, and with valves to keep the water, after it has en¬ 
tered the gills, from returning to the mouth. So that the 
mouths of Fishes may be said to be armed at both ends 
with teeth-bearing jaws. A few Fishes, as the Sturgeon, 
are toothless; but, as a class, they have an extraordinary 
dental apparatus—not only the upper and lower jaws, but 
even the palate, tongue, and throat being sometimes stud¬ 
ded with teeth. Every part of the mouth is evidently 
designed for prehension and mastication. Lips are usu¬ 
ally present; but the tongue is often absent, or very small, 
and as often aids respiration as ingestion. 

Amphibians and Eeptiles have a wide mouth; even the 
insect-feeding Toads and the Serpents can stretch theirs 
enormously. True fleshy lips are wanting; hence the 
savage aspect of the grinning Crocodile. With some ex¬ 
ceptions, as Toads and Turtles, the jaws are armed with 
teeth. Turtles are provided with horny beaks. The 
tongue is rarely absent, but is generally too thick and 
short to be of much use. In the Toad and Frog it is sin¬ 
gularly extensile: rooted in front and free behind, it is 
shot from the mouth with such rapidity that the insect is 
seized and swallowed more quickly than the eye can fol¬ 
low. The Chameleon’s tongue is also extensile. Snakes 


62 


COMPARATIVE ZOOLOGY. 



Fig. 26.—Mouth of the Crocodile: d, tongue; e, glands; /, inferior, and g, superior, 
valve, separating the cavity of the mouth from the throat, h. 


have a slender forked tongue, consisting of a pair of mus¬ 
cular cylinders, which is solely an instrument of touch. 

Birds are without lips or teeth, the jaws being covered 
with horn forming a beak. This varies greatly in shape, 
being extremely wide in the Whippoorwill, remarkably 
long in the Pelican, stout in the Eagle, and slender in the 
Hummer. It is hardest in those that tear or bruise their 
food, and softest in water-birds. The tongue is also cov¬ 
ered with a horny sheath, and generally spinous, its chief 
function being to secure the food when in the mouth. 
It is proportionally largest and most fleshy in the Parrots. 

The main characteristics of the mammalian mouth are 
flesh lips and mobile cheeks. 23 In the duck-billed Mon- 
otremes lips are wanting, and in the Porpoises they are 
barely represented. But in the herbivorous quadrupeds 
they, with the tongue, are the chief organs of prehension ; 
in the carnivorous tribes they are thin and retractile; 
while in the Whale the upper lip falls down like a cur¬ 
tain, overlapping the lower jaw several feet. As a rule, 
the mouth is terminal; but in the Elephant, Tapir, Hog, 





HOW ANIMALS EAT. 


63 


and Shrew, the upper lip blends with the nose to form a 
proboscis, or snout. The mouth is comparatively small 
in the Elephant and in gnawing animals like the Squir¬ 
rel, wide in the Carnivores, short in the Sloth, and long in 
the Ant-eater. Teeth are usually present, but vary in 
form and number with the habits of the animal. The 
Ant-eater is toothless, and the Greenland Whale has a 
sieve made of horny plates. The 
tongue conforms in size and shape 
with the lower jaw, and is a muscu¬ 
lar, sensitive organ, which serves 
many purposes, assisting in the 
prehension, mastication, and swal¬ 
lowing of food, besides being an 
organ of taste, touch, and speech. 

Its surface is covered with minute 
prominences, called papillae, which 
are arranged in lines with mathe¬ 
matical precision. In the Cats, 
these are developed into recurved Fig 27 
spines, which the animal uses in 
cleaning bones and combing its 
fur. Similar papillae occur on 
the roof and sides of the mouth 
of the Ox and other Kuminants. 

In some animals, as the Hamster 
and Gopher, the cheeks are developed into pouches in 
which the food may be carried. These may be lined with 
hair. The tongue is remarkably long in the Ant-eater 
and Giraffe, and almost immovable in the Gnawers, Ele¬ 
phants, and Whales. 

3. The Teeth of Animals. —Nearly all animals have 
certain hard parts within the mouth for the prehension or 
trituration of solid food. If these are wanting, the legs 
are often armed with spines, or pincers, to serve the same 



■Human Tongue and ad¬ 
jacent parts: a, lingual papillae: 
&, papillae forming V-shaped 
lines ; cf, fungiform papillae; e , 
filiform papillae; g, epiglottis; 
m, uvula, or conical process, 
hanging from the soft palate, 
n; o, hard palate; r, palatine 
glands, the mucous membrane 
being removed; v, section of the 
lower jaw. 


64 


COMPARATIVE ZOOLOGY. 


purpose, as in the Horse-shoe Crab; or the stomach is 
lined with “gastric teeth,” as in some marine Snails; or 
the deficiency is supplied by a muscular gizzard, as in 
Birds, Ant-eaters, and some Insects. Even the Lobster 
and Crab, in addition to their complicated oral organs, 
have the stomach furnished with a powerful set of teeth. 

The Sea-urchin is the first of animals, and almost 
the only one below Worms and Mollusks, which exhibits 


anything like a 
dental apparatus. 
Five calcareous 
teeth, having a 
wedge - shaped 
apex, each set in 
a triangular pyr¬ 



amid, or “jaw,” 
are moved upon 
each other by a 



inent of levers and muscles. Instead of moving up and 
down, as in Yertebrates, or from right to left, as in Ar¬ 
thropods, they converge towards the centre, and the food 
passes between ten grinding surfaces. 

The Kotifers (a group of minute Worms) have a curi¬ 
ous pair of horny jaws. That which answers to the lower 
jaw is fixed, and called the “ anvil.” The upper jaw con¬ 
sists of two pieces called “ hammers,” which are sharply 
notched, and beat upon the “anvil” between them (Fig. 
219). 

The horny-toothed mandibles of Insects, already men¬ 
tioned, are prehensile, and also serve to divide the food. 

The three little white ridges in the mouth of the Leech 
are the convex edges of horny semicircles, each bordered 
by a row of nearly a hundred hard, sharp teeth. When 
the mouth, or sucker, is applied to the skin, a sawing 


HOW ANIMALS EAT. 


65 






Ftg. 29.— Teeth and Masticatory Apparatus of Gastero¬ 
poda : A, portion of odontophore, or “ tongue,” of Vel- 
utina, enlarged ; B, portion of odontophore of Whelk 
(Buecinum undatum), magnified —the entire tongue 
has 100 rows of teeth ; C. head and odontophore of Lim¬ 
pet (Patella vulgata ); D, portion of same, greatly mag¬ 
nified, to show the transverse rows of siliceous teeth. 


movement is given 
to the horny ridges, 
so that the “bite” 
of the Leech is real¬ 
ly a saw-cut. 

The dentition of 
the univalve Mol- 
lusks, or the Snails, 
is generally lingual, 
i. e ., it consists of 
microscopic teeth, usually siliceous and amber-colored, 

planted in rows on the tongue. 
The teeth are, in fact, the ser¬ 
rated edges of minute plates. 
The number of these plates va¬ 
ries greatly; the garden Slug 
has 160 rows, with 180 teeth 
in each row. 

All living Birds, and some 
other Vertebrates, as Ant-eat¬ 
ers, 24 Turtles, Tortoises, Toads, 
and Sturgeons, have no teeth. 
Their place is often supplied 
by a horny beak, a muscular 
gizzard, or both structures. 

In a few Vertebrates, horny 
plates take the place of teeth, 
as the Duck Mole ( Ornitho- 
rhynchus) and Whalebone 
Whale. In the former, the 
plates consist of closely set ver- 

Fig. 30.^-Section of one half of the Up- i p 11 . n ' n fLp lo+- 

per Jaw of a Whale ( Balcenoptera ), tlca ! HOllOW tUDeS , in tne ml 

showing baleen-plates: a, superior {- er baleen, Or whalebone, 

maxillary bone; b, ligamentous gum ’ # 1 7 

attaching the horny body of the ba- plates, triangular in shape, and 
leen-plate, e; d, fringe of bristles; e, . , . . , , 

smaller plates. fringed on the inner side, hang 

5 




66 


COMPARATIVE ZOOLOGY. 


in rows from the gums of the upper jaw. In some Whales 
there are about 300 plates on each side. 25 

True teeth, consisting mainly of a hard, calcareous sub¬ 
stance called dentine , are found only in back-boned ani¬ 
mals. They are distinct from the skeleton, and differ 
from bone in containing more min- 
e eral matter, and in not showing, 
under the microscope, any minute 
cavities, called lacunae. A typical 
tooth, as found in Man, consists of 
a central mass of dentine , capped 
with enamel and surrounded on 
the fang with cement. The first 
tissue is always present, while the 
others may be absent. It is a mixt¬ 
ure of animal and mineral matter 

Fia. 31.—Section of Human Mo- , . . . „ . 

iar, enlarged: k, crown; n, disposed in the form ot extremely 

demiU’ c”cemem;Tp»l£ fine tllbeS and Cells > 80 minute a S to 
cavit y- prevent the admission of the red 

particles of blood. One modification of it is ivory, seen 
in the tusks of Elephants. Enamel is the hardest tissue 
of the body, and contains not more than two per cent, of 
animal matter. It consists of six-sided fibres set side by 
side, at right angles to the surfaces of the dentine. Ce¬ 
ment closely resembles bone, and is present only in the 
teeth of the higher animals. 

Teeth are usually confined to the jaws; but the num¬ 
ber, size, form, structure, position, and mode of attachment 
vary with the food and habits of the animal. As a rule, 
animals developing large numbers of teeth in the back 
part of the mouth are inferior to those having fewer teeth, 
and those nearer the lips. The teeth of Mammals only 
have fangs. 

The teeth of Fishes present the greatest variety. In 
number, they range from zero to hundreds. The Hag- 



HOW ANIMALS EAT. 



67 

fish (. Myxine ) has a single tooth on the roof of the mouth, 
and two serrated plates on the tongue; while the mouth 
of the Pike is crowded with teeth. In some we find 
teeth short and blunt, in the shape of cubes, or prisms, 
arranged like mosaic work. Such pavement-teeth (seen 
in some Rajs) are fitted for grinding sea-weed and crush¬ 
ing shell-fish. But the cone 
is the most common form: 
sometimes so slender and close 
as to resemble plush, as in the 
Perch; or of large size, and 
flattened like a spear - head 
with serrated edges, as in the 
Shark; but more often like the 

Fig. 32.— Jaws and Pavement-teeth of a 

canines of Mammals, curved Ray iMyUoUt^ 

inward to fit them for grappling. In the Shark, the 
teeth are confined to the fore-part of the mouth; in the 
Carp, they are all situated on the bones of the throat; in 
the Parrot-fish, they occupy both back and front; but in 
most Fishes the teeth are developed also on the roof, or 
palate, and, in fact, on nearly every bone in the mouth. 
They seldom appear (as in the Salmon) on the upper max¬ 
illary. As to mode of attachment, the teeth are generally 
anchylosed (fastened by bony matter) to the bones which 
support them, or simply bound by ligaments, as in the 
Shark. In a few Fishes, the teeth consist of flexible car¬ 
tilage ; but almost invariably they are composed of some 
kind of dentine, enamel and eement being absent. 

Of Amphibians and Reptiles, Toads, Turtles, and Tor¬ 
toises are toothless; Frogs have teeth in the upper jaw 
only; Snakes have a more complete set, blit Saurians pos¬ 
sess the most perfect dentition. The number is not fixed 
even in the same species: in the Alligator it varies from 
72 to 88. The teeth are limited to the jawbones in the 
higher forms (Saurians); but in others, as the Serpents, 












68 


COMPARATIVE ZOOLOGY. 


they are planted also in the roof of the month. With 
few exceptions, they are conical and curved (Fig. 33). In 
the Serpents they are longest and sharpest; and the ven¬ 
omous species have two or more fangs in the upper jaw. 


These fangs contain a canal, 
through which the poison 
is forced by muscles which 
compress the gland. The 
bones to which they are at¬ 
tached are movable, and the 


s 



f 



snake: g, gland, with duct, leading to 
the fang, f; m, elevator muscles of the 
jaw, which, in contracting, compress the 
gland; s, salivary glands on the edge of 
the jaws; n, nostril. 


the act of striking. As a 


rule, the teeth of Reptiles are simply soldered to the bone 
which supports them, or lodged in a groove; but those of 
Crocodiles are set in sockets. Reptilian teeth are made 
of dentine and a thin layer of cement, to which is added 
in most Saurians a coat of enamel on the crown. 

In the majority of Mammals, the teeth are limited in 
number and definite in their forms. The number ranges 
from 1 in the Narwhal (but the longest tooth in the king¬ 
dom) to 220 in the Dolphin. The average is 32, occur¬ 
ring in Ruminants, Apes, and Man; but 44 (as in the 
Hog and Mole) is called the typical or normal number, 
and this number is exceeded only in the lower groups. 
When very numerous, the teeth are of the Reptilian type, 
small, pointed, and of nearly equal size, as in the Porpoise. 
In the higher Mammals, the teeth are comparatively few, 
and differ so much in size, shape, and use, that they can 
be classed into incisors, canines, premolars, and molars. 
Such a dental series exhibits a double purpose, prehension 
and mastication. The chisel-shaped front teeth are fitted' 
for cutting the food, and hence called incisors. These 
vary in number : the Lion has six in each jaw; the Squir* 


HOW ANIMALS EAT. 


69 


rel has two in each jaw, but remarkably developed; the 
Ox has none in the upper jaw, and the Elephant none in 
the lower; while the Sloth has none at all . 26 The canines , 
so called because so prominent in the Dog, are conical, 
and, except in Man, longer than the other teeth. They 
are designed for seizing and tearing; and they are the 
most formidable weapons of the wild carnivores. There 



Fig. 34.—Skull of the Babirusa, or Malayan Hog, showing growth and curvature of 

the canines. 


are never more than four. They are wanting in all Ro¬ 
dents, and in nearly all herbivorous quadrupeds. The 
molars , or grinders, vary greatly in shape, but closely cor¬ 
respond with the structure and habits of the animal, so 
that a single tooth is sufficient to indicate the mode of 
life and to identify the species . 27 In the Ruminants, Ro¬ 
dents, Horses, and Elephants, the summits of the molars 
are flat, like mill-stones, with transverse or curving ridges 




70 


COMPARATIVE ZOOLOGY. 


of enamel. In the Cats and Dogs, they are narrow and 
sharp, passing by each other like the blades of scissors, 
and therefore cutting, rather than grinding, the food. 
The more purely carnivorous the species, and the more 
it feeds upon living prey, the fewer the molars. In ani¬ 
mals living on mixed diet, as the Hog and Man, the 
crowns have blunt tubercles. Premolars, or bicuspids, 
are those which were preceded by milk-teeth; the true, 
or back, molars had no predecessors. 

The dentition of Mammals is expressed by a formula, 
which is a combination of initial letters and figures in 



Fig. 35.— Teeth of the right lower jaw of aduTt male Chimpanzee (Troglodytes nigei% 
natural size. The molar series does not form a curve, as iu Man. 

fractional form, to show the number and kind of teeth 
on each side of both jaws. Thus, the formula for Man 



The teeth of Mammals are always restricted to the 
margins of the jaws, and form a single row in each. But 
they rarely form an unbroken series . 58 The teeth im¬ 
planted in the premaxillary bone, and in the correspond¬ 
ing part of the lower jaw, whatever their number, are in¬ 
cisors. The first tooth behind the premaxillary, if sharp 
and projecting, is a canine. 

Each tooth has its particular bony socket .* 9 The molars 


HOW ANIMALS EAT. 


71 


may be still farther strengthened by having two or more 
diverging fangs, or roots, a feature peculiar to this class. 
The incisors and canines have but one fang; and those 
that are perpetually growing, as the incisors of Rodents 
and Elephants, have none at all. The teeth of flesh-eat¬ 
ing Mammals usually consist of hard dentine, surrounded 
on the root with cement and capped with enamel. In the 
herbivorous tribes, they are very complex, the enamel and 
cement being inflected into the dentine, forming folds, 
as in the molar of the Ox, or plates, as in the compound 
tooth of the Elephant. This arrangement of these tissues, 
which differ in hardness, secures a surface with prominent 



Fig. 36. —Upper Molar Tooth of Indian Elephant ( Elepha* Indicus), showing trans¬ 
verse arrangement of dentine, d, with festooned border of enamel plates, e; c, 
cement"; one-third natural size. 


ridges, well adapted for grinding. The cutting teeth of 
the Rodents consist of dentine, with a plate of enamel on 
the anterior surface, and the unequal wear preserves a 
chisel-like edge. Enamel is sometimes wanting, as in the 
molars of the Sloth and the tusks of the Elephant. 

In Fishes and Reptiles, there is an almost unlimited 
succession of teeth; but Mammalian teeth are cast and 
renewed but once in life. 

Vertebrates use their teeth for the prehension of food, 
as weapons of offence or defence, as aids in locomotion, 
and as instruments for uprooting or cutting down trees. 
But in the higher class they are principally adapted for 
dividing or grinding the food . 30 While in nearly all other 




72 


COMPARATIVE ZOOLOGY. 


Vertebrates the food is bolted entire, Mammals masticate 
it before swallowing. Mastication is more essential in the 
digestion of vegetable than of animal food; and hence we 
find the dental apparatus most efficient in the herbivorous 
quadrupeds. The food is most perfectly reduced by the 
Rodents. 

Teeth, as we shall see, are appendages of the skin, not 
of the skeleton, and, like other superficial organs, are es¬ 
pecially liable to be modified in accordance with the hab¬ 
its of the creature. They are, therefore, of great zoologi¬ 
cal value; for, such is the harmony between them and 
their uses, the naturalist can predict the food and general 
structure of an animal from a sight of the teeth alone. 
For the same reason, they form important guides in the 
classification of animals; while their durability renders 
them available to the paleontologist in the determination 
of the nature and affinities of extinct species, of which 
they are often the sole remains. Even the structure is 
so peculiar that a fragment will sometimes suffice. 

4. Deglutition, or How Animals Swallow.—In the 
lowest forms of life, the mouth is but an aperture opening 
immediately into the body-cavity, and the food is drawn 
in by ciliary currents. But in the majority of animals, a 
muscular tube, called the gullet, or oesophagus, intervenes 
between the mouth and stomach, the circular fibres of 
which contract, in a wave-like manner, from above down¬ 
ward, propelling the morsel into the stomach. 81 In the 
higher Mollusks, Arthropods, and Vertebrates, deglutition 
is generally assisted by the tongue, which presses the food 
backward, and by a glairy juice, called saliva, which facil¬ 
itates its passage through the gullet. 33 Vertebrates have 
a cavity behind the mouth, called the throat, or z>harynx, 
which may be considered as a funnel to the oesophagus. 33 
In air-breathers, it has openings leading to the windpipe, 
nose, and ears. In Man, as in Mammals generally, the 


HOW ANIMALS EAT. 


73 


process of deglutition is in this wise: the food, masticated 
by the teeth and lubricated by the saliva, is forced by the 
tongue and cheeks into the pharynx; the soft palate keep¬ 
ing it out of the nasal aperture, and the valve-like epiglot¬ 
tis falling down to form a bridge over the opening to the 
windpipe. The moment the pharynx receives the food, 
it is firmly grasped, and, the muscular fibres contracting 
above it and left lax below it, it is rapidly thrust into the 
oesophagus. Here, a similar movement (the peristaltic) 
strips the food into the stomach . 34 The rapidity of these 
contractions transmitted along the oesophagus may be ob¬ 
served in the neck of a Horse while drinking. 

Deglutition in the Serpents is painfully slow, and some¬ 
what peculiar. For how is an animal, without limbs or 
molars, to swallow its prey, which is often much larger 
than its own body? The Boa-constrictor, e.g., seizes the 



Fig. 37.—Skull of Boa-constrictor: 1, frontal; 2, prefrontal; 4, postfrontal; 5, basi- 
occipital; 6, sphenoid; 7, parietal; 12, squamosal; 13, prootic; 17, premax¬ 
illary; 18, maxillary; 20, nasal; 24, transverse; 25, internal pterygoid; 34, den¬ 
tary, lower jaw; 35, angular; 36, articular; a, quadrate; s, prenasal; v, petrosal. 


head of its victim with its sharp recurving teeth, and 
crushes the body with its overlapping coils. Then, slow¬ 
ly uncoiling, and covering the carcass with a slimy mu¬ 
cus, it thrusts the head into its mouth by main force, the 
mouth stretching marvellously, the skull being loosely put 





74 


COMPARATIVE ZOOLOGY. 


together. One jaw is then unfixed, and the teeth with¬ 
drawn by being pushed forward, when they are again 
fastened farther back upon the animal. The other jaw 
is then protruded and refastened; and thus, by successive 
movements, the prey is slowly and spirally drawn into 
the wide gullet. 


CHAPTER IX. 

THE ALIMENTARY CANAL. 

The Alimentary Canal is the great route by which 
nutritive matter reaches the interior of the body. It is 
the most universal organ in the animal kingdom, and the 
rest are secondary or subservient to it. In the higher an¬ 
imals, it consists of a mouth, pharynx, gullet, stomach, 
and intestine. 

It is a general law, that food can be introduced into 
the living system only in a fluid state. While plants send 
forth their roots to seek nourishment from without, ani¬ 
mals, which may be likened to plants turned outside in, 
have their roots (called absorbents) directed inward along 
the walls of a central tube or cavity. This cavity is for 
the reception and preparation of the food, so that animals 
may be said to carry their soil about with them. The 
necessity for such a cavity arises not only from the fact 
that the food, which is usually solid, must be dissolved, so 
as to make its way through the delicate walls of the cav¬ 
ity into the system, but also from the occurrence of inter¬ 
vals between the periods of eating, and the consequent 
need of a reservoir. For animals, unlike plants, are thrown 
upon their own wits to procure food. 

The Protozoa, as the Amoeba and Infusoria, can hardly 



THE ALIMENTARY CANAL. 


75 


be said to have a digestive canal. The animal is here 


composed of a single cell, in which the food is digested. 
The jelly-like Amoeba passes the food through the firmer 
outer layer ( ectosarc ) into the more fluid inner part ( endo- 
sarc\ where it is digested. The Infusoria, which have a 
cuticle, and so a more definite form, possess a mouth, or 
opening, into the interior of their cell-body, and at least 
a definite place where the excrement is passed out. But 
we cannot call this cell-cavity a digestive tract. 

In the higher animals, the alimentary canal is a contin¬ 
uation of the skin, which is reflected inward, as we turn 
the finger of a glove. 35 We find every grade of this re¬ 
flection, from the sac of the Hydra to the long intestinal 
tube of the Ox. So that food in the stomach is still out¬ 
side of the true body. 

The simplest form of such a digestive tract is seen in 
the Hydra (Fig. 191). Here the body is a simple bag, 
whose walls are composed of two layers of cells (ectoderm 
and endoderm). A 



mouth leads into the 
cavity, and serves as 
well for the outlet of 


matter not wanted. v 


The endodermal cells 
furnish the juices by 
which the food is di- 


gested and absorb the 


nutritious portions of 
it. There is no rad¬ 


ical difference, how¬ 


ever, between the two 



of respiratory water from one compartment to an- 


Ul J ** ''*** ----I-—- 

the former ectoderm other; d, mouth leading to gastric cavity, e. 




76 


COMPARATIVE ZOOLOGY. 


lias digested the food and the former endoderm has taken 
on the functions of the outer layer. The Polyps have 
also but one external opening; but from this hangs down 
a short tube, open at both ends, reaching about half-way 
to the bottom of the body-cavity. Such an arrangement 
would be represented by a bottle with its neck turned 
inward. In this suspended sac, which is somewhat con¬ 
stricted at the extremities, digestion takes place; but the 
product passes freely into all the surrounding chambers, 
along with the water for respiration. The Medusae, or 
Jelly-fishes, preserve the same type of a digestive appara¬ 
tus ; but the sac is cut off from the general cavity, and 
numerous canals radiate from it to a circular canal near 
the margin of the disk. In the Star-fishes (Fig. 126), we 
find a great advance. The sac-like stomach sends off two 
glandular branches to each arm, which doubtless furnish 
a fluid to aid in digestion (so-called hepatic coeca). There 
is also an anus present in some forms, but it hardly serves 
to pass off the waste matter. 

Thus far we have seen but one opening to the digestive 
cavity, rejected portions returning by the same road by 
which they enter. But a true alimentary canal should 
have an anal aperture distinct from the oral. The sim¬ 
plest form of such a canal is exhibited by the Sponge, in 
its system of absorbent pores for the entrance of liquid, 
and of several main channels for its discharge. The 
apparatus, however, is not marked off from the general 
cavity of the body, and digestion is not distinct from cir¬ 
culation. 36 

The Sea-urchin presents us with an important advance 
—one cavity with two orifices; and the complicated ap¬ 
paratus of higher animals is but the development of this 
type. This alimentary canal begins in a mouth well pro¬ 
vided with teeth and muscles, and extends spirally to its 
outlet, which generally opens on the upper, or opposite, 


THE ALIMENTARY CANAL. 


77 


surface. Moreover, while in some of the Worms the canal 
is a simple tube running through the axis of the cylindri¬ 
cal body from oral orb 
fice to anal aperture, the 
canal of the Sea-urchin 
shows a distinction of 
parts,foreshadowing the 
pharynx, gullet, stom¬ 
ach, and intestines. Both 
mouth and vent have 
muscles for constriction 
and expansion; and, as 

f-Lp vpnt is nn Hip snm Fie. 39.— Diagrammatic Section of a Sea-urcliin 
me vent IS on me sum {Echinm): a >mou th; b, oesophagus; c, stom¬ 
ach ; cl, intestine; /, madreporiform tubercle ; 
< 7 , stone-canal; h, ambulacral ring; k, Polian 
vesicles, which are probably reservoirs of fluid; 
m, ambulacral tube; o, anus; p, ambulacra, 
with their contractile vesicles; r, nervous ring 
around the gullet; s, two nervous trunks, the 
right terminating, at anal pole, in a small gan¬ 
glion ; t, blood-vascular rings connected by v, 
the contractile heart; w, two arterial trunks ra¬ 
diating from the anal ring; x, an ovary open¬ 
ing at the anal pole in a genital plate, y; z , 
spines, with their tubercles. 



mit of the shell, and the 
latter is covered with 
spines, the ejected par¬ 
ticles are seized by del¬ 
icate forks {jpedicella- 
rice ), and passed on from 
one to the other down 
the side of the body, till they are dropped off into the 
water . 37 

The Worms present us with a great range of structure 
in the digestive tract. It is sometimes almost as simple 
as that of the Hydra—a mere sac. The Earth-worm has 
a tube running straight through the body, divided into 
pharynx, oesophagus, crop, gizzard, and sacculated intes¬ 
tine. The Leech has large sacs on each side of the intes¬ 
tine. The Sea-worms have the pharynx armed with teeth, 
and some have glandular coeca attached to the intestine. 
The plan is that of a straight tube extending from mouth 
to anus. In Myriapods and larvse of Insects, the same 
general plan is continued, the canal passing in a straight 
line from one extremity to the other, but showing a divis¬ 
ion into gullet, stomach, and intestine . 38 Crustacea, like 








COMPARATIVE ZOOLOGY. 


78 



the Lobster, have a short gullet leading to a large cav¬ 
ity, situated in the front of the animal, which is a giz¬ 
zard, rather than 
stomach, as it has 
thick muscular 
walls armed with 
teeth. A well- 
marked constric¬ 
tion separates this 
organ from the in¬ 
testine. The liver 
is highly devel¬ 
oped ; instead of 
numerous folli¬ 
cles, there is a 
large bilaterally 
symmetrical or¬ 
gan, divided into 
th ree lobes on each 
side, pouring its 
secretion into the 
upper part of the 
intestine, which is 
the true stomach. 

Among Insects, 
there is great vari¬ 
ation in the form 
and length of the 

Pig. 40.—Anatomy of a Caterpillar: g, h, oesophagus; h , . 

i, stomach; k, hepatic vessels; l, m, intestine; q, r, sal- Canal. IneiOllOW- 
ivary glands; p, salivary duct; a, b, c, longitudinal : no . ~ ar ,. a 
tracheal trunks; d, e, air-tubes distributed to the vis- 1IJ fe P^rib Cdll geil- 
cera; /, fat-mass; v, x, y, silk-secretors; z, their ex- grailV be distin- 
cretory ducts, terminating in t, the spinneret, or fu- t * 

suius. guished: gullet, 

crop, gizzard, stomach, and large and small intestines, with 
many glandular appendages. The crop, gizzard, and large 
intestine are sometimes absent, especially in the carnivorous 







THE ALIMENTARY CANAL. 


79 



species. In Bees, the crop is called the u honey - bag.” 
The gizzard is found in Insects having mandibles, and is 


Fig. 41.— Alimentary canal of a Beetle: 
a, pharynx; b, gullet, leading to crop, 
c, gizzard, d, and stomach, e; f, deli¬ 
cate urinary tubes; g, intestine; h, 
other secreting organs. 


Fig. 42. — Alimentary Canal of the Bee 
(Apis mellifica ): a, gullet; b, crop; c, d, 
stomach; e, small intestine; /, large in¬ 
testine ; g, anal orifice; h , urinary ves¬ 
sels ; i, auxiliary glands. 


frequently lined with rows of horny teeth, which are spe¬ 
cially developed in Grasshoppers, Crickets, and Locusts. 
The intestines are remarkable for their convolutions. In¬ 


sects have no true liver; but its functions are performed 
by little cell-masses on the inside of the stomach. 39 

The alimentary canal of Spiders is short and straight, 
the pharynx and gullet being very minute. The stomach 
is characterized by sending out tubular prolongations, and 


n' n" h c h o 



Fig 43 .—Anatomy of a Sphinx Moth: n, nervous cord ; n', brain sending off nerves 
to the lege, l', l", l'", and for the wings at n "; h, dorsal vessel, or heart; c, crop; 
s, stomach; i, intestines; o, reproductive organs; o', oviduct; 8-20, segments. 










80 


COMPARATIVE ZOOLOGY. 


the intestines end in a large bladder-like expansion. Scor¬ 
pions have no stomachal cavity—a straight intestine passes 
directly through the body. 

In bivalve Mollnsks, like the Clam, the month opens 
into a short oesophagus which leads into the stomach, 
which lies imbedded in a large liver, and the intestine, 
describing a few turns, passes directly through the heart. 40 
In the univalve Mollnsks, like the Snail, the gullet is long,, 
and frequently expands into a crop; the stomach is often 
double, the anterior being a gizzard provided with teeth 
for mastication; the intestine passes through the liver, 
and ends in the fore-part of the body, usually on the right 
side. 

The highest Mollusks, as the Cuttle-fish and Nautilus, 
exhibit a marked advance. A mouth with powerful man¬ 
dibles leads to a long gullet, which ends in a strong mus¬ 
cular gizzard resembling that of a fowl. 41 Below this is a 
cavity, which is either a stomach or duodenum ; it receives 



Pig. 44.—Alimentary Canal of the Oyster: a , stomach 
laid open; d , liver; 6, c, d,f, convolutions of the intes¬ 
tine; g, anal aperture; n, o, auricle and ventricle; l, 
m, adductor muscle; h , k , lobes of month divided to 
show the venous canals at the base of the gills. 


the bile from a 
large liver. The 
intestine is a tube 
of uniform size, 
which, after one or 
two slight curves, 
bends up,and opens 
into the “funnel” 
near the month. 

Fishes have a 
simple, short, and 
wide alimentary 
canal. The stom¬ 
ach is separated 
from the intestine 
by a narrow “ py¬ 
loric” orifice, or 


THE ALIMENTARY CANAL. 


81 



t io. 45—Anatomy of a Gasteropod (Snail): a , mouth ; 6, foot; c, amis; d , lung? 
e, stomach, covered above by the salivary glands ; /, intestine ; g , liver; h , heart; 
i, aorta; j, gastric artery; Z, hepatic artery; k , artery of the foot; m, abdominal 
cavity, supplying the place of a venous sinus; n, irregular canal communicating 
with the abdominal cavity, and carrying the blood to the lung; o, vessel carry¬ 
ing blood from the lung to the heart. 

valve, blit is not so clearly distinguished from the gullet, 
so that regurgitation is easy . 42 Indeed, it is common for 



Pm. 46 _Anatomy of a Lameilibranch (Mactra): a , shell; h, mantle; c, tentacles, or 

Ups; d, mouth; e, nerves; /, muscles; g, anterior, and n, posterior ganglion; h , 
liver; i, heart: k, stomach; Z, intestine passing through the heart; m, kidney; o, 
anal end of the intestine; p , exhaleut, aud q, inhalent respiratory tubes, or si¬ 
phons ; r, gills; s, foot. 


6 














82 


COMPARATIVE ZOOLOGY. 


Fishes to disgorge the indigestible parts of their food, and 
some, as the Carp, send the food back to the pharynx to 
be masticated. The stomach is usually bent, like a si¬ 
phon ; but the intestine is nearly straight, and without 
any marked distinction into small and large. Its append¬ 
ages are a large liver and a rudimentary pancreas. 

In the Amphibians, as the Frogs, the digestive appara¬ 
tus is very similar to that of Fishes; but the two kinds 
of intestines can be more readily 
distinguished. The Reptiles gen¬ 
erally have a long, wide gullet, 
which passes insensibly into the 
stomach, and a short intestine 
(about twice the length of the 
body) very distinctly divided into 
small and large by a constric¬ 
tion. 43 The vegetable - feeding 
Tortoises have a comparatively 
long intestinal tube; and the 
Serpents have a slender stomach, 
but little wider than the rest of 

Fio. 47.—Anatomy of a Cepbaiopod the alimentary canal. 

(diagram): a, tentacles; 6, masti- J 

catory apparatus; c, eye; d, sali- The Stomach of the Crocodile 
vary gland; e, nervous ganglia; • i .i , . . 

/, oesophagus; g, internal shell, or 1S inore Complex than any llltll- 

mentioned. It resembles 

tbat 0f the Cuttle-fish,but offers 

chial chamber ; s,branchial heart ; a Still more Striking analogy to 
t, systemic heart; v, mantle. 53,7 

the gizzard of a Bird, having 
very thick walls, and the muscular fibres radiating pre¬ 
cisely in the same manner, so that, in this respect, the 
Crocodile may be considered the connecting link between 
Reptiles and Birds. 44 In Crocodiles also the duodenum, 
with which the intestine begins, is first distinctly defined. 
Into this part of the intestine the liver and pancreas, or 
sweet-bread, pour their secretions. Furthermore, in the 







THE ALIMENTARY CANAL. 


83 


lower animals, the intestines lie more or less loose in the 
abdomen; but in the Crocodile, and likewise in Birds and 
Mammals, they are supported by a membrane called mes¬ 
entery. 



Fig. 48. —Anatomy of the Carp: br, branchiae, or gill-openings; c, heart; /, liver; vn, 
vn', swimming-bladder; ci f ,intestinal canal; o, ovarium; u , ureter; a, anus; o', 
genital opening; u', opening of ureter. The side-view shows the disposition of 
the muscles in vertical flakes. 













84 COMPARATIVE ZOOLOGY. 

In Birds, the length of the alimentary canal varies with 
their diet, being greatest in those living on grain and fruit. 
The gullet corresponds in length with the neck,, which is 
longest in the long-legged tribes, and in width with the 
food. In those that swallow large fish entire, the gullet 
is dilatable, as in Snakes. In nearly all Birds, the food is 
delayed in some cavity before digestion : thus, the Pelican 
has a bag under the lower jaw, and the Cormorant lias a 

capacious gullet, 
where they store 
up fishes; while 
those that gorge 
themselves at in¬ 
tervals, as the 
Vulture, or feed 
on seeds and 
grai ns,as the Tur¬ 
key,have a pouch, 
called the crop, 
developed near 
the lower end of 
the gullet. 45 The 
Ostrich, Goose, 
Swan, most of 
the Waders, and 

Fig. 49 .—Stomach of the Crocodile: a r mwscnlar fibres ra- • 

diating from a central tendon, b; d, commencement of tlie trUlt 01 m- 
duodenom; c r oesophagus; /,intestine. Sect eating Birds, 

which find their food in tolerable abundance, and take it 
in small quantities, have no such reservoir. Pigeons have 
a double crop. 

In all Birds, the food passes from the gullet into the 
proventriculus , or stomach proper, where it is mixed with 
a “gastric juice” secreted from glands on the surface. 
Thence it goes into the gizzard, an oval sac of highly 
muscular texture, and lined with a tough, horny skin. 48 



THE ALIMENTARY CANAL. ,35 



: Hie gizzard is most highly developed, and of a deep-red 
color, in the Scratchers and flat-billed Swimmers (as Fowls 
■ and. Swans); but comparatively thin and feeble in Birds 
of. Prey (as the Eagle), 

The gizzard, is follow¬ 
ed .by the intestines, 
which are longer than 
those of Reptiles: the 
small intestine begins 

' <0 

with a loop (the duo¬ 
denum), and is folded 
, several times upon it- 
• self; the large intestine 
is short and! straight, 
terminating in the sole 
outlet of the body, the 
cloaca l A liver and 

pancreas are always 
attached to the upper 
part of the small in¬ 
testine. 

The alimentary ca¬ 
nal in Mammals is 
clearly separated into 
four distinct cavities: 


the pharynx, or throat; 
the oesophagus, or gul¬ 
let; the stomach ; and 
the intestines. 


The pharynx is more 
complicated than in 
Birds. It is a funnel- 
shaped bag, having 
seven openings lead¬ 
ing into it: two from 


Fig. 50. — Digestive Apparatus of the Fowl: 1, 
tongue; 2, pharynx; 3, 5, cesophagus; 4, crop; 
6 , proventriculus; 7, gizzard; 8,9,10, duodenum ; 
11,12, small intestine ; 13, two caeca (analogue O f f 
the colon of mammals); 14, their insertion into 
the intestinal tube; 15, rectum; 16, cloaca; 17, 
anas; 18, mesentery; 19,20, left aud right lobes 
of liver; 21, gall-bladder; 22, insertion of pan¬ 
creatic and biliary ducts; 23, pancreas; 24, lung; 
25, ovary; 26, oviduct. 





8G 


COMPARATIVE ZOOLOGY. 





the nostrils, and two from 
the ears; one from the 
windpipe, guarded, by 
the epiglottis; one from 
the mouth, with a fleshy 
curtain called the soft pal¬ 
ate ; and one from the 
oesophagus. It is the nat¬ 
ural passage for food be¬ 
tween the mouth and the 
oesophagus, and of air be¬ 
tween the nostrils and 
windpipe. Like the 
mouth, it is lined with a 
soft mucous membrane. 

The oesophagus is a 
long and narrow tube, 
formed of two muscular 
layers: in the outside one, 
the fibres run length¬ 
wise ; in the other, they 
are circular. It is lined 
with mucous membrane. 
While in all Fishes, Rep¬ 
tiles, and Birds the ven¬ 
tral chamber is one, in 
Mammals it is divided, 
by a partition called the 
diaphragm , into two cav¬ 
ities — the thorax, con¬ 
taining the heart, lungs, 


Fig. 51.—Digestive Apparatus of Man (diagram): 1, tongue; 2, pharynx; 3, (Esopha¬ 
gus ; 4, soft palate; 5, larynx; G, palate; 7, epiglottis; 8, thyroid cartilage; 9, 
beginning of spinal marrow; 10, 11, 12, vertebne, with spinous processes; 13, 
cardiac orifice of stomach; 14, left end of stomach ; 18, pyloric vaive; 19, 20, 21, 
duodenum; 22, gall-bladder; 27, duct from pancreas; 28,29, jejunum of intestine; 
30. ileum; 34, coecum; 36, 37, 38, colon, or large intestine; 40, rectum. 








THE ALIMENTARY CANAL. 


87 


etc.; and the abdomen, containing the stomach, intes¬ 
tines, etc. The oesophagus passes through a slit in the 



Fig. 52.—Ideal Section of a Mammalian Vertebrate: A, pectoral, or fore limb; B 
pelvic, or hind limb: a, mouth; 6, cerebrum; c, cerebellum; d, nose; e, eye; f 
ear; g, oesophagus; h, stomach ; i, intestine; j, diaphragm, or midriff; k, rectum 
or termination of intestine; l, anus; m, liver; n , spleen; o, kidney; p, sympa 
thetic system of nerves; 3, pancreas; r, urinary bladder; a, spinal cord; u, ure 
ter; v, vertebral column; w, heart; a;, lung; y, trachea, or windpipe; z, epi 
glottis. 


diaphragm, and almost immediately expands into the 
stomach. 

In the majority of Mammals, the stomach is a muscular 
bag of an irregular- oval shape, lying obliquely across the 
abdomen. In the Flesh-eaters, whose food is easy of solu¬ 
tion, the stomach is usually simple, and lies nearly in the 
course of the alimentary ca¬ 
nal ; but in proportion as the 
food departs more wddely 
in its composition from the 
body itself, and is therefore 
more difficult to digest, we 
find the stomach increasing- 
in size and complexity, and 
turned aside from the gen¬ 
eral course of the canal, so as 
to retain the food a longer 
time. The inlet, or open¬ 
ing, into the oesophagus is called cardiac ; the outlet, or 



Fig. 53.— Section of Horse’s Stomach: A, 
left sac; B, right sac; C, duodenum. 




88 


COMPARATIVE ZOOLOGY. 


opening, leading into the intestines is called pyloric. In 
the Carnivores, Apes, and most odd-toed quadrupeds, the 
stomach resembles that of Man. That 
of the toothless Ant-eater has the 
lower part turned into a kind of giz¬ 
zard for crushing its food. The Ele¬ 
phant’s is subdivided by numerous 
folds. In the Horse, it is constricted 
„ in the middle; and in the Rodents 

Fig. 54. —Stomach of the # 7 

Porpoise: c, cardiac; p, Porpoises, and Kangaroos, the con- 
pylonc ’ strietion is carried so far as to make 

two or three sections. But animals that chew the cud 
(Ruminants) have the most complex stomach. It is di¬ 
vided into four peculiar chambers: First, the paunch 
(rumen), the largest 
of all, receives the 
half-masticated food 
when first swallowed. 

The inner surface is 
covered with papillae, 
except in the Camel, 
which has large cells 

for storing up water, fig. 55. —Stomach of the Lion: c, cardiac orifice, or 
From this, the food entrance of (esophagus s *. .pyloric. 

passes into the honey-comb stomach ( reticulum ), so named 
from its structure. Liquids swallowed usually go directly 
to this cavity, without passing through the paunch, and 





Fiq. 56.—Complex Stomach of a Ruminant: a, gullet; b, rumen, or paunch; c, reticu¬ 
lum ; d, psalterium, or manyplics; e, abomaeus; /, pylorus leading to duodenum. 


THE ALIMENTARY CANAL. 


89 


hence it is sometimes called the water-bag. Here the 
food is made into little balls, and returned to the mouth 
to undergo a thorough mastication. When finally swal¬ 
lowed, it is directed, by a groove from the oesophagus, to 
the third, and smallest, cavity, the manyplies ( psalterium ), 
named from its numerous folds, which form a strainer to 
keep back any undivided food; and thence it passes into 
the true stomach ( abomasus ), from which, in the calf, the 
rennet is procured for curdling milk in the manufacture 
of cheese. This fourth cavity 
is like the human stomach in 
form and function, and is the 
only part which secretes gastric 
juice. The rumen and reticu¬ 
lum are rather dilatations of the 
oesophagus than parts of the 
stomach itself; while the latter 
is divided by constriction into 
two chambers, the psalterium 
and abomasus, as in many other 
animals. 

In structure, the stomach re¬ 
sembles the oesophagus. The 
smooth outside coat ( verito - 

. n Fig. 57. —Vertical Section of the 

neum) IS a reflection of the Coats of the stomach: 1, surface 

membrane which lines the whole 
abdomen. The middle, or mus¬ 
cular, coat consists of three lay¬ 
ers of fibres, running length¬ 
wise around and obliquely. The successive contraction and 
relaxing of these fibres produce the worm-like motion of 
the stomach, called peristaltic. The innermost, or mucous, 
membrane, is soft, velvety, of a reddish-gray color in Man, 
and filled with multitudes of glands, which secrete the 
gastric juice. The human stomach, when distended, will 



of mucous membrane, and mouths 
of gastric follicles; 2, gastric tubu- 
li, or follicles ; 3, dense connective 
tissue; 4, submucous tissue; 5, 
transverse muscular fibre; 6, longi¬ 
tudinal muscular fibre ; 7, fibrous, 
or serous, coat. 












90 


COMPARATIVE ZOOLOGY. 


bold about five pints; that of the Kangaroo is as long 
as its body. 

The intestinal canal in Mammals begins at the pjdoric 
end of the stomach, where there is a kind of valve or cir¬ 
cular muscle. Like the stomach, it varies greatly, accord¬ 
ing to the nature of the food. It is generally longest in 
the Yegetable-feeders, and shortest in the Flesh-feeders. 
The greater length in the former is due to the fact that 


vegetable food requires a longer 
time for digestion, and that a great¬ 
er bulk of such food is required to 
obtain a given quantity of nutri¬ 
ment. The intestines measure 150 
feet in a full-grown Ox, while they 
are but three times the length of 
the body in the Lion, and six times 
in Man. Save in some lower 
forms, as the Whales, there are 
two main divisions, the “ small ” 
and “large” intestines, at the 
junction of which is a valve. The 



former is the longer of the two, 
„ and in it digestion is amnrilatari. 



from the body. The beginning of 


the small intestine is called the duodenum , into which 
the ducts from the liver and pancreas open. The intes¬ 
tinal canal has the same structure as the stomach, and by 
a peristaltic motion its contents are propelled downward. 
The inside surface of the small intestine is covered with 
a host of thread-like processes (villi), resembling the pile 
of velvet. 







HOW ANIMALS DIGEST. 


91 


In taking this general survey of the succession of forms 
;which the digestive apparatus presents among the princi¬ 
pal groups of animals, we cannot fail to trace a gradual 
specialization . First, a simple sac, one orifice serving as 
inlet for food and outlet for indigestible matter; next, a 
short tube, with walls of its own suspended in the body- 
cavity ; then a canal passing through the body, and, there¬ 
fore, having both mouth and vent; next, an apparatus for 
mastication, and a swelling of the central part of the canal 
into a stomach, having the special endowment of secreting 
gastric juice; then a distinction between the small and 
large intestine, the former thickly set w T ith villi, and re¬ 
ceiving the secretions of large glands. We also notice 
that food, the means of obtaining it, the instruments for 
mastication, and the size and complexity of the aliment¬ 
ary canal, are closely related. 


CHAPTER X. 

HOW ANIMALS DIGEST. 

The object of the digestive process is the reduction 
of food into such a state that it can be absorbed into the 
system. For this purpose, if solid, it is dissolved; for 
fluidity is a primary condition, but not the only one. 
Many soluble substances have to undergo a chemical 
change before they can form parts of the living body. 
If albumen or sugar be injected into the veins, it will not 
be assimilated, but be cast out unaltered. 

To produce these two essential changes, solution and 
transmutation, two agencies are used — one mechanical, 
the other chemical. The former is not always needed, 
for many animals find their food already dissolved, as the 



92 


COMPARATIVE ZOOLOGY. 


Butterfly; but solid substances, to facilitate their solu¬ 
tion, are ground or torn into pieces by teeth, as in Man; 
by jaws, as in the Lobster; or by a gizzard, as in the 
Turkey. 

The chemical preparation of food is indispensable. 47 It 
is accomplished by one or more solvent fluids secreted in 
the alimentary canal. The most important, and one al¬ 
ways present, is the gastric juice, the secretion of which 
is restricted to the stomach, when that cavity exists. In 
the higher animals, numerous glands pour additional flu¬ 
ids into the digestive tube, as saliva into the upper part 
or mouth, and bile and pancreatic juice into the upper 
part of the intestine. In fact, the mucous membrane, 
which lines the alimentary canal throughout, abounds with 
secreting glands or cells. 

The Digestive Process is substantially the same in all 
animals, but it is carried further in the more highly de¬ 
veloped forms. In the Infusoria, the food is acted upon 
by some secretion from the walls of the body-cavity, the 
exact nature of which is unknown. In the Star-fish and 
Sea-urchin, we find two solvents — a gastric juice, and 
another resembling bile; but the two appear to mingle in 
the stomach. Mollusks and Arthropods show a clear 
distinction between the stomach and intestine, and the 
contents of the liver are poured into the latter. There 
are, therefore, two stages in the digestive act: first, the 
food is dissolved by the gastric juice in the stomach, form¬ 
ing chyme ; secondly, the chyme, upon entering the intes¬ 
tine, is changed into chyle by the action of the bile, and 
is then ready to be absorbed into the system. 

In Vertebrates, a third solvent is added, the pancreatic 
juice, which aids the bile in completing digestion. But 
Mammals and Insects have a still more perfect and elab¬ 
orate process; for in them the saliva of the mouth acts 
chemically upon the food; while the saliva in many other 


HOW ANIMALS DIGEST. 


93 


animals has no other office, so far as we know, than to 
moisten the food for swallowing. 

Taking Man as an example, let ns note the main facts 
in the process. During mastication, by which the relative 
surface is increased, the food is mixed with saliva, which 
moistens the food , 48 and turns part of the starch into 
grape-sugar. Passed into the stomach, the food meets the 
gastric juice. This is acid, and, first, stops the action of 
the saliva; secondly, by means of the pepsin which it con¬ 
tains, and the acid, it dissolves the albumen, fibrine, and 
such constituents of the food. This solution of albumi¬ 
noids is called a peptone , and is especially distinguished 
from other such solutions by its diff nsibility— i. e., the ease 
with which it passes through a membrane. These pep¬ 
tones, with the sugars of the food, whether original or the 
product of the action of the saliva, are absorbed from the 
stomach. The food, while in the stomach, is kept in con¬ 
tinual motion, and, after a time, is discharged in gushes 
into the intestine. The name chyme is given to the pulpy 
mass of food in the stomach. In the intestine the chyme 
meets three fluids—bile, pancreatic juice, and intestinal 
juice. All of these are alkaline, and at once give the acid 
chyme an alkaline reaction. This change permits the 
action of the saliva to recom¬ 
mence, which is aided by the 
pancreatic and intestinal juices. 

The pancreatic juice has much 
more important functions. It 
changes albuminoid food into 
peptones, and probably breaks 
up the fats into very small par¬ 
ticles, which are suspended in 
the fluid chyle. This forms an Fig. 59.—Chyle Corpuscles, x 500. 
emulsion , like milk, and causes the chyle to appear whit¬ 
ish. The bile has important functions, but little under* 



94 


COMPARATIVE ZOOLOGY. 


stood. It saponifies part of the fats, so that they are dis-* 
solved, and prevents the.food from decomposing during 
the process of digestion and absorption. The chyle is 
slowly driven through the small intestine by the creeps 
ing, peristaltic motion of its walls , 49 the nutritious portion 
being taken up by the absorbents, as described in the next 
chapter, while the undigested part remaining is discharged 
from the large intestine . 50 


CHAPTER XI. 

THE ABSORBENT SYSTEM. 

The nutritive matter (chyle), prepared by the digestive 
process, is still outside of the organism. How shall it 
enter the living tissue ? 

In animals, like the Infusoria and Polyps, whose digest¬ 
ive department is not separated from the body-cavity, the 
food, as soon as dissolved, mingles freely with the tissues 
and organs it has to nourish. In the higher Invertebrates 
having an alimentary canal, .the chyle, passes, by simple 
transudation, through the walls of the canal directly into, 
the soft tissues, as in Insects, or is absorbed from the canal 
by veins in contact with it, as in Sea-urchins, Mollusks, 
Worms, and Crustaceans, and then distributed through 
the body. 

In Vertebrates only do we find a special absorbent sys¬ 
tem. Three sets of vessels are concerned in the general 
process by which fresh material is taken up and added to 
the blood: Capillaries, Lacteals, and Lymphatics. 
Only the two former draw material from the alimentary 
canal. 

It is a general law that the food is absorbed as fast as 



THE ABSORBENT SYSTEM. 


95 


it is dissolved, and, therefore, there is a constant loss in 
the passage down the canal. In the mouth and oesoph¬ 
agus, the absorption is slight; but much of that which 
has yielded to the gastric juice, with most of the water, is 
greedily absorbed by the capillaries of the stomach, and 
made to join the current of blood which is rushing to the 
liver. Absorption by the capillaries also takes place from 
the skin and lungs. Medicinal or poisonous gases and 
liquids are readily introduced into the system by these 
channels. 

We have seen that the oily part of the food passes un¬ 
changed from the stomach into the small intestine, where, 
acted upon by the pancreatic juice, it is cut up into ex¬ 
tremely minute particles, and that the undigested albumi¬ 
noids and starches are digest¬ 
ed in the intestine. Two 
kinds of absorbents are pres¬ 
ent in the intestine, lacteals 
and blood-capillaries. Both 
the lymphatic and blood sys¬ 
tems send vessels into the 
velvety villi 61 with which the 
intestine is lined. The blood- 

. j i , Fig. 60. —Lacteal System of Mammal: a. 

capillaries lie towards the out- descending aorta, or principal artery ; 

side of the villus and the 
lacteal in the centre. The 

albuminoids and sugars are /, lacteal, or mesenteric, glands, 
chiefly absorbed by the blood-vessels and go to the liver. 
The fats pass on into the lacteals, which receive their 
name from the milky appearance of the chyle. These 
lacteals unite into larger trunks, which lie in the mesen¬ 
tery (or membrane which suspends the intestine from the 
back wall of the abdomen), and these pour their contents 
into one large vessel, the thoracic duct , lying along the 
backbone, and joining the jugular vein in the neck. 



96 


COMPARATIVE ZOOLOGY. 



The laeteals are only a special part of the great lym¬ 
phatic system, which absorbs and carries to the thoracic 

duct matter from all parts 
of the body . 62 The lymph 
is a transparent fluid having 
many white blood corpus¬ 
cles. It is, in fact, blood, 
minus the red corpuscles, 
while chyle is the same fluid 
rendered milky by numer¬ 
ous fat - globules. During 
the intervals of digestion, 
the laeteals carry ordinary; 
lymph. This fluid is the 
overflow of the blood — the 
plasma and white corpus¬ 
cles which escape from the 
blood capillaries, and are not 
needed by the tissues in 
which they are. This sur¬ 
plus overflow is returned to 
the blood by the lymphatics. 
The current is kept up by 
the movements of the body, 
and in many Vertebrates, as 
Frogs and Fishes, by lymph 

receptaculum chyli. The oval bodies 7 

are glands. hearts. 

Like the roots of Plants, the absorbent vessels do not 
commence with open mouths; but the fluid which enters 
them must traverse the membrane which covers their mi¬ 
nute extremities. This membrane is, however, porous, 
and the fluids pass through it by the forces of filtration 
and diffusion. How the fat gets into the laeteals is not 
yet well understood, but the laeteals are themselves rhyth¬ 
mically contractile , 63 and force the absorbed chyle tow- 


Fig. 61.—Principal Lymphatics of the Hu¬ 
man Body: a, union of left jugular and 
subclavian veins; b, thoracic duct; c, 




THE BLOOD OF ANIMALS. 97 

ards the heart. The valves of the lymphatics prevent its 
return. 


CHAPTER XII. 

* THE BLOOD OF ANIMALS. 

The Blood is that fluid which carries to the living tis¬ 
sues the materials necessary to their growth and repair, 
and removes their waste and worn-out material. The 
great bulk of the body is occupied with apparatus for the 
preparation and circulation of this vital fluid. 

The blood of the lower animals (Invertebrates) differs 
so widely from that of Man and other Vertebrates, that 
the former were long supposed to be without blood. In 
them the blood is commonly colorless; but it has a bluish 
cast in Crustaceans; reddish, yellowish, or greenish, in 
Worms; and reddish, greenish, or brownish, in Jelly¬ 
fishes. The red liquid which appears when the head of 
a Fly is crushed is not blood, but comes from the eyes. 
In Vertebrates, the blood is red, excepting the white- 
blooded fish, Amphioxus . 84 

As a rule, the more simple the fabric of the body, the 
more simple the nutritive fluid. In unicellular animals 
(as Protozoa), in those whose cells are comparatively inde¬ 
pendent (as Sponges), and in small and lowly organized 
animals (like Hydra), there is no special circulating fluid. 
Each cell feeds itself either directly from particles of 
food, or from the products of digestion. In Polyps and 
Jelly-fishes, the blood is scarcely different from the prod¬ 
ucts of digestion, although a few blood-corpuscles are pres¬ 
ent. But in the more highly organized Invertebrates the 
blood is a distinct tissue, coagulating, and containing 
white corpuscles. The blood of the Vertebrates, appar- 

T 



98 


COMPARATIVE ZOOLOGY. 


ently a clear, homogeneous fluid, really consists of minute 
grains, or globules, of organic matter floating in water. 


If the blood of a Frog 
be poured on a filter of 
blotting-paper, a trans¬ 
parent fluid (called plas¬ 
ma) will pass through, 
leaving red particles, re- 



*0 sembling sand, on the 
upper surface. Under 
| the microscope, these 
particles prove to be 
cells, or flattened disks 
(called corpuscles ), con- 


c 


b ^b 


Fio. 62.— Red Blood-corpnecles of Man: a, shows ^ 
circular contour; b, a biconcave section; c, a taining a nucleus ; SOine 
group in chains. ■, , 

are colorless, and others 


group in chains. 


red. The red disks have a tendency to run together into 
piles; the colorless ones remain single. Meanwhile, the 
plasma separates into two parts by coagulating; that is, 
minute fibres form, consisting of fibrine , leaving a pale 
yellowish fluid, called serum.™ Had the blood not been 
filtered, the corpuscles and fibrine would have mingled, 
forming a jelly-like mass, known as clot. Further, the 
serum will coagulate if heated, dividing into hardened 
albumen and a watery fluid, called serosity , which contains 
the soluble salts of the blood. 

These several parts may be expressed thus: 



Llood 


albumen. 

serosity=water and salts. 


If now we examine the nutritive fluid of the simplest 
animals, we find only a watery fluid containing granules. 
In Radiates and the Worms and Mollusks, there is a sim¬ 
ilar fluid, with the addition of a few white corpuscles. But 


THE BLOOD OF ANIMALS. 


99 


there is little fibrine, and, therefore, it coagulates feebly or 
not at all. In the Arthropods and higher Mollusks, the 
circulating fluid contains 
colorless nucleated cells, 
and coagulates. 56 In Ver¬ 
tebrates, there are, in ad¬ 
dition to the plasma and 
white corpuscles of In¬ 
vertebrates, red corpus¬ 
cles, to which their blood 
owes its peculiar hue. 

In Fishes, Amphibians, 

Reptiles, and Birds, i. e ., 
all oviparous Vertebrates, 
these red corpuscles are Fio.es.-NucieatedBiood-ceiisofaFro^x 250. 

nucleated; but in those of Mammals, no nucleus has been 
discovered. 57 

All blood-corpuscles are microscopic. The white are 
more uniform in size than the red; and generally smaller 
(except in Mammals), being about 
of an inch in diameter. The 
red corpuscles are largest in Amphib^ 
ians (those of Proteus being the ex¬ 
treme, or -j-iir of an inch), next in 
Fishes, then Birds and Mammals. The 
smallest known are those of the Musk- 
Fig. 64 .— Elliptical corpus- deer. In Mammals, the size agrees 
a white prominence at the with the size oi the animal only Wlth- 

centre ‘ in a natural order; but in Birds the 

correspondence holds good throughout the class, the larg¬ 
est being found in the Ostrich, and the smallest in the 
Humming-bird. In Man, they measure of an inch, 
so that it would take 40,000 to cover the head of a 
pin. 

As to shape, the colorless corpuscles are ordinarily glob- 








100 


COMPARATIVE ZOOLOGY. 


ular, or sac-like, in all animals; but they are constantly 
changing. The form of the red disks is more permanent, 
although they are soft and elastic, so that they squeeze 



Fig. 65 .—Comparative Size and Shape of the red Corpuscles of various Animals. 


through very narrow passages. They are oval, circular, 
or angular, in Fishes; oval in Reptiles, Birds, and the 
Camel tribe; and circular in the rest of Mammals. They 
are double-convex when nucleated, and double-concave 
when circular and not nucleated. 

Blood is always heavier than water; but is thinner in 
cold-blooded than in warm-blooded animals, in herbivores 
than in carnivores. The blood of Birds, which is the hot¬ 
test known, being 10° higher than Man’s, is richest in red 
corpuscles. In Man, they constitute about one half the 
mass of blood. The white globules are far less numerous 
than the red; they are relatively more abundant in venous 
than arterial blood, in the sickly and ill-fed than in the 
healthy and vigorous, in the lower Vertebrates than in 
Birds and Mammals. Their number is subject to great 

















THE BLOOD OF ANIMALS. 


101 


variations, increasing rapidly after a meal, and falling as 
rapidly. 

There is less blood in cold-blooded than in warm-blood¬ 
ed animals; and the larger the animal, the greater is the 



Fig. C6 .— Capillary Circulation in the Web of a Frog’s Foot, X 100 : a, b, small veins ° 
d, capillaries in which the oval corpuscles are seen to follow one another in sin¬ 
gle series; c, pigment-cells in the skin. 

proportion of blood to the body. Man has abont a gallon 
and a half, equal to one thirteenth of his weight. The 
heart of the Greenland Whale is a yard in diameter. 

The main Office of the Blood is to supply nourish¬ 
ment to, and take away waste matters from, all parts of 
the body. It is at once purveyor and scavenger. In its 
circulation, it passes, while in the arterial half of the cap¬ 
illaries, within an infinitesimal distance of the various tis¬ 
sues. The plasma, carrying the nutritive matter needed, 
exudes through the walls of the capillary tubes; the tissue 
assimilates or makes like to itself whatever is suitable for 
its growth and repair; and the lymphatics (the escape- 







102 


COMPARATIVE ZOOLOGY. 


pipes) take up any surplus, and return it to the blood. 
At the same time, the venous part of the capillary net¬ 
work absorbs the waste products of the tissues, expelling 
the gases by the lungs, and the solid matters by the skin 
and kidneys. The special function of the several constit¬ 
uents of the blood is not wholly known. The colorless 
corpuscles in Vertebrates are supposed to be the source of 
the red disks. The latter are the carriers of oxygen, 
which is taken up by their red matter (haemoglobin) in 
the lungs, and given up to the tissues. The same office is 
performed by the blue coloring - matter (heemocyanin) in 
the blood of certain Invertebrates, as the Squid and Lob¬ 
ster. The carbon dioxide is taken up by the plasma. 

Like the solid tissues, the blood, which is in reality a 
liquid tissue, is subject to waste and renewal, to growth 
and decay. The loss is repaired from the products of 
digestion, carried to the blood by the lacteals, or absorbed 
directly by the capillaries of the digestive tract. The 
white corpuscles are probably prepared in many parts of 
the body, especially the liver, spleen, and lymphatic glands. 
In the lower organisms, the nutritive food is prepared by 
contact with the tissues, without passing through special 
organs. Lymph differs from blood chiefly in containing 
less albumen and fibrine, and no red disks. Chyle is 
lymph loaded with fat globules, and is found in the lac¬ 
teals and vessels connected with them during the absorp¬ 
tion of food containing fat. 


THE CIRCULATION OF THE BLOOD. 


103 


CHAPTER XIII. 


THE CIRCULATION OF THE BLOOD. 


The Blood is kept in continual motion in order to 
nourish and purify the body and itself. For as life means 
work, and work brings waste, there is constant need of 
fresh material to make good the loss in every part of the 
system, and of the removal of matter which is no longer 
fit for use. 

In the very lowest animals, where every part of the 
structure is equally capable 
of absorbing the digested 
food and is in contact with 
it, there is no occasion for 
any circulation, although 
in them even the blood is 
not allowed to stagnate. 

But in proportion as the 
power of absorption is con¬ 
fined to certain parts, the 
more is the need and the 
greater the complexity of 
an apparatus for convey¬ 
ing the nutritive fluid to 
the various tissues. 

In nearly all animals, 
the nutritive fluid is con¬ 
veyed to the various parts 
of the body by a system 

of tubes, called blood-ves - TT „ „ 

sels. The higher forms cur in pairs, as represented. 



104: COMPARATIVE ZOOLOGY. 

have two sets— arteries and veins , in which the blood 
moves in opposite directions, the former carrying blood 
from a central reservoir or heart , 
the latter taking it to the heart. 
In the Vertebrates, the walls of 
these tubes are made of three 
coats, or layers, of tissue, the arte¬ 
ries being elastic, like rubber, and 
many of the veins being furnished 
with valves. 68 The great artery 
coming out of the heart is called 
aorta, and the grand venous trunk, 
entering the heart on the opposite 
side, is called vena cava. Both 
sets divide and subdivide until 
their branches are finer than hairs; 
and joining these finest arteries 
and finest veins are intermediate 
microscopic tubes, called capilla¬ 
ries (in Man about -g-^Va- of an inch 
F veC &7 and‘capiliarST' 2 iu diameter). 6 * In these only, so 

seen in the muscles of a Dog. an( } d e li ca te are their Walls, 

does the blood come in contact with the tissues or the air. 

In those Vertebrates which have lungs there are two 
sets of capillaries, since there are two circulations—the 
systemic , from the heart around the system to the heart 
again, and the pulmonary , from the heart through the 
respiratory organ back to the heart. This double course 
may be illustrated by the figure 8. In gill-bearing animals 
there are capillaries in the gills, but not a double circu¬ 
lation. 

There is no true system of blood-vessels below the 
Star-fish, The simplest provision for the distribution of 
the products of digestion is shown by the Jelly-fish, whose 
stomach sends off radiating tubes (Fig. 197). 











THE CIRCULATION OF THE BLOOD. 


105 


The first Approach to a Circulatory System is made 
by the Star-fish and the Sea-urchin. A vein runs along 
the whole length of the alimentary tube, to absorb the 
chyle, and forms a circle around each end of the tube. 
These circular vessels send off branches to various parts 
of the body; but as they are not connected by a net-work 
of capillaries, there can be no circuit (Fig. 39). 

A higher type is exhibited by the Insects. If we ex¬ 
amine the back of any thin-skinned Caterpillar, a long 
pulsating tube is seen running beneath 
the skin from one end of the body to 
the other. This dorsal vessel, or heart, 
as it is called, is open at both ends, and 
divided by valves into compartments, 
permitting the blood to go forward, 
but not backward. Each compartment 
communicates by a pair of slits, guard¬ 
ed by valves, with the body - cavity, so 
that fluids may enter, but cannot es¬ 
cape. “ Circulation ” is very simple. 

We have seen that the chyle exudes 
through the walls of the alimentary ca¬ 
nal directly into the cavity of the abdo¬ 
men, where it mingles with the blood 
already there. This mixed fluid is 
drawn into the dorsal tube through the Fxg - 69.—Part of the Dor- 

0 sal Vessel, or Heart, of 

valvular openings as it expands; and a Cockchafer bisected : 

., . ,. „ ,, ., «, b, muscular walls; 

Upon its contraction, all tll6 SiuG-ValVOS valves between the 

are closed, and the fluid is forced tow- 

ards the head. Passing out at the front or . ifices communicating 

& with the general cavity 

opening, it is again diffused among and of the abdomen, 
between the tissues of the body. The blood, therefore, 
does not describe a circle in definite channels so as to re¬ 
turn constantly to its point of departure. 

Many worms (as the Earthworm) have a pulsating tube 









106 


COMPAKATIVE ZOOLOGY. 


extending from tail to liead above the alimentary canal, 
a similar tube on the ventral side through which the blood 
returns, and cross-tubes in every segment. In the Lob¬ 
ster and Crab, Spider and Scorpion, the dorsal tube sends 



Fig. 70.—Circulation in a Lobster: a , heart; 6, artery for the eyes; c, artery for an¬ 
tennae; d, hepatic artery; e, superior abdominal artery; /, sternal artery; g, ve¬ 
nous sinuses transmitting blood from the body to the branchiae, h, whence it 
returns to the heart by the brauchio-cardiac vessels, i. 

off a system of arteries (not found in Insects); but the 
blood, as it leaves these tubes, escapes into the general 
cavity, as in other Arthropoda. The Lobster and Crab, 
however, show a great advance in the concentration of 
the propelling power into a short muscular sac. 

A third development of the circulatory system is fur¬ 
nished by the Mollusks. Comparatively sluggish, they 
need a powerful force-pump in the form of a compact 
heart. In the Oyster and Snail (Figs. 44,45), we find such 
an organ having two cavities—an auricle and a ventricle, 
one for receiving, and the other for distributing, the blood. 
The auricle injects the blood into the ventricle, which 
propels it by the arteries to the various organs. Thence 
it passes, not immediately to the veins, as in higher ani¬ 
mals, but into the spaces around the alimentary canal. A 
part of this is carried by vessels to the gills or lung, and 
then returned with the unpurified portion to the auricle. 
The whole of the blood, therefore, does not make a com¬ 
plete circuit. The Clam has a similar heart, but with two 
auricles. 








THE CIRCULATION OF THE BLOOD. 


107 

A still higher form is seen in the Cuttle-fish, the high- 
est of the Invertebrates. This animal has a central heart, 
with a ventricle and two auricles, 
and, in addition, the veins which 
collect the blood from the system 
to send it back to the heart by 
the way of the gills are furnished 
with two branchial hearts , which 
accelerate the circulation through 
those organs. Many of the arte¬ 
ries and veins are joined by cap- f 
illaries, but not all; so that in 
no invertebrate animal is the 
blood returned to the heart by a 
continuous closed system of blood- g 
vessels. 

As a rule, in all animals hav¬ 
ing any circulation at all, the cur¬ 
rent always takes one direction. 

This is generally necessitated by 
valves. But a curious exception 
is presented by the Ascidians, 
whose tubular heart is valveless, 
and the contractions occur alter¬ 
nately at one end and then the 
other; so that the blood oscil¬ 
lates to and fro, and a given ves¬ 
sel is at one time a vein and at 
another an artery, 
spect it resembles the foetal heart 
of higher animals (Fig. 279). 

In Vertebrates only is the cir¬ 
culating current strictly confined 
to the blood-vessels; in no case does it escape into the 
general cavity of the body. In other respects, there is 



Tn flii a Fig. 71 —Circulating Apparatus in 

x l o l tJ- the yigjj. branchial artery ; 6, 
arterial bulb; c, ventricle; d, au¬ 
ricle ; e, venous sinus; f, portal 
vein; g, intestine; h, vena cava; 
i, branchial vessels; k, dorsal ar¬ 
tery, or aorta; l , kidneys; m, 
dorsal artery. 














108 


COMPARATIVE ZOOLOGY. 


no great advance in the apparatus of the lowest Verte¬ 
brates over that of the highest Mollusks. The heart of 

Fishes, as in the Oyster, has 
two cavities, but its position 
is reversed. Instead of driv¬ 
ing arterial blood over the 
body, it receives the return¬ 
ing, or venous, blood, and 
sends it to the gills. Re¬ 
collected from the gills, the 
blood is passed into a large 
artery, or aorta , along the 
back, which distributes it by 
a complex system of capil¬ 
laries among the tissues. 

amide; a, aorta, or main artery. These Capillaries Unite with 

the ends of the veins which pass the blood into the auri¬ 
cle 60 (Fig. 48). 

In Amphibians and in Reptiles generally (as Frogs, 
Snakes, Lizards, and Turtles), the heart has three cavities 
—two auricles and one ventricle. The venous blood from 
the body is received into the right auricle, and the puri¬ 
fied blood from the lungs into the left. Both throw their 
contents into the ventricle, which pumps the mixed blood 
in two directions—partly to the lungs, and partly around 
the system. Circulation is, therefore, incomplete, since 
the whole current does not pass through the lungs, and 
three kinds of blood are found in the body—arterial, ve¬ 
nous, and mixed. In many animals, however, arrange¬ 
ments exist which nearly separate the venous from the 
arterial blood. 

The ventricle of Reptiles is partially divided by a par¬ 
tition. In the Crocodile, the division is complete, so that 
there are really four cavities—two auricles, and two ven¬ 
tricles. But both ventricles send off aortas which cross 



THE CIRCULATION OF THE BLOOD. 


109 



one another, and at that point a small aperture brings the 
two into communication. The venous and arterial cur¬ 
rents are, therefore, mixed, 
but not within the heart, as 
in the other Reptiles, nor so 
extensively. In the structure 
of the heart, as well as in that 
of the gizzard, Crocodiles ap¬ 
proach the Birds. 

The Highest Form of the 
Circulating System is pos¬ 
sessed by the warm-blooded 
Vertebrates, Birds and Mam- fig. 73—Heart of the uugoug, a four- 

1 vr i chambered heart, the parts being more 

mals. JNOt a drop OI blood separated than in higher animals: E, 
.v.right ventricle; L, left ventricle; D, 

can make the circuit ot the rl j hl >nricle . F ,p U , monal . y aru;ry : 
body without passing through K > left aiiriele; A » aorta - 
the lungs, the circulation to and from those organs being 
as perfect as the distribution of arterial blood. The heart 
/ 3 * 9 consists of four cavities — a 

\ » i 

right auricle and ventricle, and 
a left auricle and ventricle. In 
other words, it is a hollow mus¬ 
cle divided internally by a ver¬ 
tical partition into two distinct 
chambers, each of which is 
again divided by a valve into 
an auricle and a ventricle. The 
work of the right auricle and 

Fig. 74. -Theoretical Section of the ven f r j 0 l e [a f 0 receive the blood 
Human Heart: a, right ventricle; v enhriOie ictene Uie UlOOU 

b, inferior vena cava; c, tricuspid from tile veins, and Send it to 
valve; d, right auricle; e, pulmona¬ 
ry veins; /, superior vena cava; g, the lllilgS ; while the Other two 
pulmonary arteries; h, aorta; k, left . . 

auricle ; l, mitral valve; m, left ven- receive the blood irom tile 
tricie; «, septum. lungs, and propel it over the 

body. The left ventricle has more to do than any other 
cavity. The two auricles contract at the same instant; 


d 





110 


COMPARATIVE ZOOLOGY. 





so also do the ventricles. The course 
of the current in Bipds and Mammals 
is as follows : the venous blood 
brought from the system is discharged 
by two or three large trunks 61 into 
the right auricle, which immediately 
forces it past a valve 62 into the right 
ventricle. The ventricle then con¬ 
tracts, and the blood rushes through 
the pulmonary artery past its semi¬ 
lunar valves into the lungs, where it 
is changed from venous to arterial, 
Fig. 75. — Plan of circuia- returning by the pulmonary veins to 
cie• b, ventricle • c, bran- the left auncle. 1 his sends it past 
the mitral valves into the left ventri- 
from the gills, d, and c le, which drives it past the semilunar 

uniting in the aorta, /; g, 1 

vena cava. valves into the aorta, and thence, by 

its ramifying arteries and capillaries, into all parts of the 
body except the lungs. 

From the capillaries, 
the blood, now changed 
from arterial to venous, 
is gathered by the veins, 
and conveyed back to 
the heart. 

The Rate of the 
Blood - current gener¬ 
ally increases with the 
activity of the animal, 
being most rapid in 
Birds. 63 In Insects, 


however, it is compara¬ 
tively slow; but this is 
because the air is taken 
to the blood—the whole 


Fig. 76 .—A, Plan of CircnTation in Amphibia and 
Reptiles; B, Plan of Circulation in Birds and 
Mammals: a, right auricle receiving venons 
blood from the system; ft, left auricle receiving 
arterial blood from the lnngs; e, c', ventricles; 
d,e,/, systemic artery, vein, and capillaries; g, 
pulmonary artery; ft, k, vein and capillaries. 







HOW ANIMALS BREATHE. 


Ill 


body being bathed in air, so that the blood has no need 
to hasten to a special organ. However, activity nearly 
doubles the rate of pulsation in a Bee. The motion in 
the arteries is several times faster than in the veins, but 
diminishes as the distance from the heart increases. In 
the carotid of the Horse, the blood moves 12£ inches per « 
second; in that of Man, 16; in the capillaries of Man, 1 
to 2 inches per minute; in those of a Frog, 1. 

The Cause of the Blood-current may be cilia, or the 
contractions of the body, or pulsating tubes or hearts. In 
the higher animals, the impulse of the heart is not the 
sole means: it is aided by the contractions of the arteries 
themselves, the movements of the chest in respiration, and 
the attraction of the tissues for the arterial blood in the 
capillaries. In the Chick, the blood moves before the 
heart begins to beat; and if the heart of an animal be 
suddenly taken out, the motion in the capillaries will 
continue as before. It has been estimated that the force 
which the human heart expends in twenty-four hours is 
about equivalent to lifting 217 tons one foot. 


CHAPTER XIY. 

HOW ANIMALS BREATHE. 

Arterial Blood, in passing through the system, both 

loses and gains certain substances. It loses constructive 

material and oxygen to the tissues. These losses are made 

good from the digestive tract and breathing organ. It 

2 *ains also certain waste materials from the tissues, which 
© 

must be got rid of. Of these waste products, one, carbon 
dioxide, is gaseous, and is passed off from the same organ 
as that where the oxygen is taken in. This exchange of 



112 


COMPARATIVE ZOOLOGY, 


gases between the animal and its surroundings is called 
Respiration. 

The First Object of Respiration, is to convert venous 
into arterial blood. It is done by bringing it to the sur¬ 
face, so that carbon dioxide may be exhaled and oxygen 
absorbed. The apparatus for this purpose is analogous to 
the one used for circulation. In the lowest animals, the 
two are combined. But in the highest, each is essentially 
a pump, distributing a fluid (in one case air, in the other 
blood) through a series of tubes to a system of cells or 
capillaries. They are also closely related to each other: 
the more perfect the circulation, the more careful the pro¬ 
vision made for respiration. 

Respiration is performed either in air or in water. 
Bo that all animals may be classed as air-breathers or 
water-breathers. The latter are, of course, aquatic, and 
seek the air which is dissolved in the water. Land-snails, 
Myriapods, Spiders, Insects, Reptiles, Birds, and Mam¬ 
mals breathe air directly; the rest, with few exceptions, 
receive it through the medium of water. In the former 
case, the organ is internal; in the latter, it is more or less 
on the outside. But however varied the organs — tubes, 
gills, or lungs—they are all constructed on the same prin¬ 
ciple—a thin membrane separating the blood from the 
atmosphere. 

< 1 ) Sponges, Infusoria* and Polyps have no separate respir¬ 
atory apparatus, but absorb air, as well as food, from the 
currents of water passing through them. 

In the Star-fish, Sea-urchin, and the like, we find the 
first distinct respiratory organs, although none are exclu¬ 
sively devoted to respiration. There are two sets of ca¬ 
nals—one carrying the nutrient fluid, and the other, radi¬ 
ating from a ring around the mouth, distributing aerated 
water, used for locomotion as well as respiration. This 
may be called the “ water-pipe system.” Besides this, 


IIOW ANIMALS BREATHE. 


113 


there are numerous gill-like fringes, which 
probably aid in respiration (Fig. 39). 

Fresh-water Worms, like the Leech and 
Earth-worm, breathe by the skin. The 
body is always covered by a viscid fluid, 
which has the property of absorbing air. 

The air is, therefore, brought into immedi¬ 
ate contact with the soft skin, underneath 
which lies a dense net-work of blood-ves¬ 
sels. 

But most water-breathing animals have 
gills. The simplest form is seen in Marine 
Worms: delicate veins projecting through 
the skin make a series of arborescent tufts 
along the side of the body; as these float 
in the water, the blood is purified. 84 Bi¬ 
valve Mollusks have four flat gills, consist¬ 
ing of delicate membranes filled with blood¬ 
vessels and covered with cilia. In the Oys¬ 
ter, these ribbon-like folds are exposed to 

the water when 
the shell opens; 
but in the Clam, 
the mantle en¬ 
closes them, forming a tube, 
called siphon , through which 
the water is driven by the 
cilia. The aquatic Gastero- 
pods (Univalves) have either 
tufts, like the Worms, or comb- 

Fig. 78. —Diagrammatic Section of a like ciliated gills ill a Cavity 

Lamellibranch (Anodon): a, lobes of i i • J , winch the 

mantle; 6 , gills, showing transverse DemnQ tlie iieaa, lO WIHOJ 

partitions; c, ventricle of hoart; d, wa t e r is admitted by a sipllOIl. 
auricles; e, pericardium; g, kid- . r . 

neys; h, venous sinus ; k, foot; A, The Cuttle-fish lias flat glllS 

epibrShiaUhamber. chambe ‘ ’ B ’ covered by the mantle; but the 

8 



Fig. 77.—Lob-worm 
( Arenicolapiscato - 
rum), a dorsibran- 
chiate, showing 
the tufts of capil¬ 
laries, or external 
gills. The large 
head is without 
eyes or jaws. 









114 


COMPARATIVE ZOOLOGY. 


water is drawn in by muscular contractions instead of by 
cilia. The end of the siphon through which it is ejected 
is called the funnel. The gills of Lobsters and Crabs are 
placed in cavities covered by the sides of the shell (cara¬ 
pace); and the water is brought in from behind by the 
action of a scoop-shaped process attached to one of the 
jaws, which constantly bales the water out at the front. 

The perfection of apparatus for aquatic respiration is 
seen in Fishes. The gills are comb-like fringes supported 
on four or five bony or cartilaginous arches, and contain 
myriads of microscopic capillaries, the object being to ex¬ 
pose the venous blood in a state of minute subdivision 
to streams of water. The gills are always covered. In 
bony fishes they are attached to the hinder side of bony 
arches, all covered by a flap of the skin, supported by 
bones (the gill-cover, or operculum ), and the water escapes 
from the opening left at its hinder edge. In Sharks, the 
gills are placed in pouches which open separately (Figs. 
164 and 287). The act of “breathing water” resembles 
swallowing, only the water passes the gills instead of en¬ 
tering the gullet. 



Fie. 79—Spiracle of an Insect, x 75. 

est and most delicate organs, so 


(2) Air-breathers have 
tracheae, or lungs. The 
former consist of two 
principal tubes, which 
pass from one end of 
the body to the other, 
opening on the surface 
by apertures,called spir¬ 
acles, resembling a row’ 
of button-holes alon<£ 
the sides of the thorax 
and abdomen, and rami¬ 
fying through the small- 
that the air may follow 



HOW ANIMALS BREATHE. 


115 


the blood wherever it circulates. To keep the pipes ever 
open, and at the same time leave them flexible, they are 
provided with an elastic spiral thread, like 
the rubber tube of a drop-light. Kespira- 
tion is performed by the movements of 
the abdomen, as may be seen in the Bee 
when at rest. This “ air-pipe system,” as 
it may be termed, is best developed in In¬ 
sects. 

The “nerves” of an Insect’s wine: con- 

& Fig. 80. — Tracheal 

sist of a tube within a tube: the inner one Tube of au insect, 

. . .... highly magnified, 

is a trachea carrying air, and the outer one, showing elastic 
sheathing it, is a blood-vessel. So perfect 8pual th,ead * 
is the aeration of the whole body, from brain to feet, 
the blood is ox} y genated at the moment when, and on the 
spot where, it is carbonized; only one kind of fluid is, 


h 



n 


Fig. 81.—Ideal Section of a Bee: a , alimentary canal; h, dorsal vessel: t, trachea; 
n, nervous cord. 

therefore, circulating — arterial. It is difficult to drown 
an Insect, as the water cannot enter the pores; but if a 
drop of oil be applied to the abdomen, it falls dead at 
once, being suffocated. The largest spiracle is usually 






116 COMPARATIVE ZOOLOGY. 


found on the thorax, as un¬ 
der the wing of a Moth: 
such may be strangled by 
pinching the thorax. 

In Millipedes and Centi¬ 
pedes, the spiracles open 
into little sacs connected 
together by tubes; in Spi¬ 
ders and Scorpions, the 
spiracles, usually four in 
.. . .. w v number, are the mouths of 

Fig. S2.— Section through a bronchial tube, * 

Lung of a Bird, magnified : a, the cavity; sacs without the tubes, aild 
b, its lining membrane supporting blood- ... 

vessels ; c, perforations at the orifices of the interior of tile SBC is 
the lobular passages, d; e, interlobular j , . « , , y i 

spaces, containing the terminal branches gatliei CQ into lOlClS. .Land- 

of the pulmonary vessels supplying the ' ;] ] spiracle, Or 

capillary plexus,/, to the meshes of which I ’ 

the air gets access by the lobular passages, aperture, Oil the left side of 

the neck, leading to a large cavity, or sac, lined with fine 
blood-vessels. These sacs represent the primitive idea of 
a lwig, which is but an infolding of the skin, divided up 
into cells, and covered with capillary veins . 65 


Fig. S3. —Part of a transverse section of a Pig’s Bronchial Twig, x 240: a, onte- 
fibrous layer; h, muscular layer; c, inner fibrous layer; d y epithelial layer with 
cilia; /, one of the neighboring alveoli. 













HOW ANIMALS BREATHE. 


117 


|_b 


Like the alimentary canal, the lungs of an animal are 
really an inflected portion of the outer surface; so that 
breathing by the skin and breathing by lungs are one in 
principle. Indeed, in many animals, especially Frogs, res¬ 
piration is carried on by both lungs and skin. 

The lungs of Yertebrates are derived from the front 
part of the alimentary canal. In some Fishes, air is swal¬ 
lowed, which passes the whole length of the digestive 
tract, and is expelled from the anus. Here 
the whole canal serves for respiration. In 
Reptiles, Birds, and Mammals the hinder 
part of the intestine develops an outgrowth 
(the allantois) during embryo-life which 
serves as the embryo’s breathing organ (Figs. 

170,171). 

All Yertebrates have two kinds of respir¬ 
atory organs in the course of their life. 

Fishes have gills; their lung (the air-blad¬ 
der) rarely serves as a functional respiratory 
organ, and is sometimes wanting. Amphibi¬ 
ans have gills while in the larval state. Some 
keep them throughout life; but all develop 
functional lungs, and also breathe by means 
of the skin. 

In the remaining Yertebrates, the allantois 
is the breathing organ of the embryo, and 
the lung is the breathing organ of the adult. 

The skin is of small or no importance in 
respiration. 

The lungs of Yertebrates are elastic mem- 

O . Fig. 84. — Lungs 

branons sacs, divided more or less into cells of a suake: a, 

. „ tt xi ■ r trachea b, its 

to increase the surface. Upon the wa.,8 ot bifurcation; c, 
the cells are spread the capillary blood-ves- ^ryT^puimJ" 
sels. The'smaller the cells, the greater the jW 
extent of surface upon which the blood is memory. 


118 


COMPARATIVE ZOOLOGY. 


exposed to the influence of the air, and, therefore, the 
more active the respiration and the purer the blood. The 
lungs are relatively largest in Reptiles, and smallest in 
Mammals. But in the cold-blooded Amphibians and Rep¬ 
tiles, the air-cells are few and large; in the warm-blooded 
Birds and Mammals, they are exceedingly numerous and 
minute . 66 In Birds and Mammals, the blood in the capil¬ 
laries is exposed to the air on all sides; in the Reptiles, 
on one only. Respiration is most perfect in Birds; they 
require, relatively to their weights, more air than Mam¬ 
mals or Reptiles, and most quickly die for lack of it. In 
Birds, respiration is not contined to the lungs; but, as in 
Insects, extends through a great part of the body. Air- 
sacs connected with the lungs exist in the abdomen and 
under the skin of the neck, wings, and legs. Even the 
bones are hollow for this purpose; so that if the wind- 



Fig. 85.— Lungs of a Frog: a, hyoid 
apparatus; 6, cartilagiuous ring at 
root of the lungs; c, pulmonary 
vessels; d, pulmonary sacs, having 
this peculiarity common to all cold¬ 
blooded air-breathers, that the tra¬ 
chea does not divide into bronchial 
branches, but terminates abruptly 
by orifices which open at once into 
the general cavity. A cartilaginous 
net-work divides the space into lit¬ 
tle sacs, on the walls of which the 
capillaries are spread. 



Fig. SC. —Distribution of Air-tubes in Mam¬ 
malian Lungs : a, larynx; 5, trachea; c, d, 
left and right bronchial tubes; e , /, g, the 
ramifications. In Man the subdivision con¬ 
tinues until the ultimate tubes are one twen¬ 
ty-fifth of an inch in diameter. Each lobule 
represents in miniature the structure of the 
entire lung of a Frog. 








119 


HOW ANIMALS BREATHE. 

pipe be tied, and an opening be made in the wing-bone, 
the bird will continue to respire. The right lung is usu¬ 
ally the larger; in some Snakes, the left is wanting en¬ 
tirely. In most Vertebrates, lungs are freely suspended ; 
in Birds, they are fastened to the back. 

The lungs communicate with the atmosphere by means 
of the trachea , or windpipe, formed of a series of cartilag¬ 
inous rings, which keep it constantly open. It begins in 
the back part of the mouth, opening into the pharynx by 
a slit, called the glottis, which, in Mammals, is protected 
by the valve-like epiglottis. The trachea passes along 
the neck in front of 
the oesophagus, and 
divides into two 
branches, or bronchi, 
one for each lung. 

In Birds and Mam¬ 
mals, the bronchial 
tubes, after entering 
the lungs, subdivide 
again into minute 
ramifications. 

Vertebrates are the Fig - 87,_skeleton of a Fr °s* 

only animals that breathe through the mouth or nos¬ 
trils. Frogs, having no ribs, and Turtles, whose ribs are 
soldered together into a shield, are compelled to swallow 
the air. Snakes, Lizards, and Crocodiles draw it into the 
lungs by the play of the ribs . 67 Birds, unlike other ani¬ 
mals, do not inhale the air by an active effort; for that is 
done by the springing-back of the breast-bone and ribs to 
their natural position. To expel the air, the breast-bone 
is drawn down towards the back-bone by muscles, which 
compresses the lungs. 

Mammals alone have a perfect thorax — i. e., a closed 
cavity for the heart and lungs, with movable walls (breast' 



120 


COMPARATIVE ZOOLOGY. 


bone and ribs) and a diaphragm, or muscular partition, 
separating it from the abdomen. 68 Inspiration (or filling 
the lungs) and expiration (or emptying the lungs) are 
both accomplished by muscular exertion ; the former, byj 
raising the ribs and lowering the diaphragm, which en¬ 


large the capacity of the 
chest, and the air rushes 


b 


9 


a 


/ 


\ 



in to prevent a vacuum; 
the latter, by the ascent of 


the diaphragm and the de- 
scent of the ribs. 


As a rule, the more ac- 


"~ h tive and more muscular an 
" d animal, the greater the de- 
('" b mand for oxygen. Thus, 
1-6’ warm-blooded animals live 


fast, and their rapidly de¬ 


caying tissues call for rapid 
v b> respiration; while in the 
\ b , cold-blooded creatures the 


waste is comparatively 


/ 


/ 


a 


Fig. SS.—Human Thorax: a, vertebral col- slow. Respiration is IllOSt 

nirm • Ti TrS riho tlio Imirot* rrnoD foloo • /» 



the ribs ; h, sternum. 


more slowly than the busy 


Bee, the Mollusk more slowly than the Fish. But respi¬ 
rations, like beats of the heart, are fewer in large Mam¬ 
mals than in small ones. An average Man inhales about 
300-400 cubic feet of air per day of rest, and much more 
when at work. 

Another result of respiration, besides the purification 
of the blood, is the production of heat. The chemical 
combination of the oxygen in the air with the carbon in 
the tissues is a true combustion ; and, therefore, the more 


SECRETION AND EXCRETION. 


121 


active the animal and its breathing, the higher its temper¬ 
ature. Birds and Mammals have a constant temperature, 
which is usually higher than that of the atmosphere (108° 
and 100° F. respectively). They are therefore called con- 
stant-temperatured or warm-blooded. Other animals do 
not vary greatly in temperature from that of their sur¬ 
roundings, and are called changeable-temperatured or cold¬ 
blooded. Still, their temperature does not agree exactly 
with that of the air or water. The Bee is from 3° to 10°, 
and the Earth-worm and Snail from 1^° to 2°, higher than 
the air. The mean temperature of the Carp and Toad is 
51°; of Man, 98°; Dog, 99°; Cat, 101°; Squirrel, 105°; 
Swallow, 111 0 . 


CHAPTER XY. 

SECRETION AND EXCRETION. 

In the circulation of the blood, not only are the nutrient 
materials deposited within the body in the form of tissue, 
but certain special fluids are separated and conveyed to 
the external or internal surfaces of the body. These flu¬ 
ids are of two kinds: some, like saliva, gastric juice, bile, 
milk, etc., are for useful purposes; others, like sweat and 
urine, are expelled from the system as useless or injurious. 
The separation of the former is called secretion; the re¬ 
moval of the latter is excretion. Both processes are sub¬ 
stantially alike. 

In the lower forms, there are no special organs, but se¬ 
cretion and excretion take place from the general surface. 
The simplest form of a secreting organ closely resembles 
that of a respiratory organ, a thin membrane separating 
the blood from the cavity into which the secretion is to 



122 


COMPARATIVE ZOOLOGY. 


be poured. Usually, however, the cells of the membrane 
manufacture the secretion from materials furnished by the 
blood. Even in the higher animals, there are such secret¬ 
ing membranes. The membranes lining the nose and ali¬ 
mentary canal and enclosing 
the lungs, heart, and joints, 
secrete lubricating fluids. 

The infolding of such a 
membrane into little sacs or 
short tubes {follicles), each 
having its own outlet, is the 
type of all secreting and ex¬ 
creting organs. The lower 
tribes have nothing higher, 
and the apparatus for pre¬ 
paring the gastric fluid at¬ 
tains no further develop¬ 
ment even in Man. When 

Fio. 89. Three plans of secreting Mem- a cluster of tllCSe follicles, 01* 
branes. The heavy line represents the 

areolar-vascular layer; the next line is SaCS, discharge theil’ Contents 
the basement, or limiting membrane; . 

and the dotted line the epithelial layer: by One Common dllCt, WC 

a shows increase of surface by simple i ._ i r» . i ,i 

plaited or fringed projections; b , five have a gland. Eut whether 

modes of increase by recesses, forming mem brai)e, follicle, Or gland, 
simple glands, or follicles; c, two forms * 5 5 

of compound glands. the organ is covered with a 

net-work of blood-vessels, and lined with epithelial cells, 
which are the real agents in the process. 

The chief Secreting Organs are the salivary glands, 
gastric follicles, pancreas, and liver, all situated along the 
digestive tract. 

1. The salivary glands, which open into the mouth, se¬ 
crete saliva. They exist in nearly all Vertebrates, higher 
Mollusks, and Insects, and are most largely developed in 
such as live on vegetable food. The saliva serves to lu¬ 
bricate or dissolve the food for swallowing, and, in some 
Mammals, aids also in digestion of starch. 68 










SECRETION AND EXCRETION. 


123 



2. The gastric follicles are minute tubes in the walls of 
the stomach secreting gastric juice. They are found in 
all Vertebrates, and in the higher Mol- 
lusks and Arthropods. In the lower 
forms, a simple membrane lined with 
cells serves the same purpose. Under 
the microscope, the soft mucous mem¬ 
brane of the human stomach presents a 
honey-comb appearance, caused by nu¬ 
merous depressions or cells. At the bot¬ 
tom of these depressions are clusters of 
spots, which are the orifices of the tubu¬ 
lar follicles. The follicles are about 
of an inch in diameter, and number mill¬ 
ions. 

3. The pancreas, or “ sweetbread,” so 

. , . - /» i. . Fig. 00.—Follicles from the 

important in the process ot digestion, stomach of a Dog, x 
when present, exists only in the Yerte- 
brates, and perhaps in the higher Mol- lumnar epithelium. 
Insks. In its structure and its secretion it closely resem¬ 
bles the salivary glands. In the Cuttle-fish, it is repre¬ 
sented by a sac; in Fish¬ 
es, by a group of follicles. 
It is proportionally larg¬ 
est in Birds whose sali¬ 
vary glands are deficient. 
The pancreatic juice en¬ 
ters the duodenum, 

4. A liver in some form 
is found in all animals 
having a distinct diges¬ 
tive cavity. In Mollusks 
and Vertebrates, it is the 
largest gland in the body. 
The higher the animal, the more compact the organ. 



Fxg. 01.—Pancreas of Man, o; g , gall-bladder 
*, cystic duct; c, duct from the liver; p, py 
loric valve; e , duodenum. 



COMPARATIVE ZOOLOGY. 


124 




Thus, in Polyps it is represented by yellowish cells lining 
the stomacli; in Insects, by cells in the wall of the stom¬ 
ach ; in Mollusks, by a cluster of sacs, or follicles, forming 
a loose compound gland. In Vertebrates, the liver is well 
defined, and composed of a multitude of lobules (which 
give it a granular appearance) arranged on the capillary 
veins, like grapes on a stem, and containing nucleated 
secreting cells. It is of variable shape, but usually two, 
three, or five lobed, and is centrally situated—in Mam¬ 
mals, just below the diaphragm. In most Vertebrates, 
there is an appendage to the liver, called the gaU-bladder , 
which is simply a reservoir for the bile when not wanted. 

The so-called liver of Invertebrates is probably more 



Fig. 92.—Liver of the Dog, F, F; D, duodenum aud iutestiues; P, pancreas; r, 
spleen; e, stomach; /, rectum; R, right kidney; B, gall-bladder; ch, cystic 
duct; F, lobe of liver dissected to show distribution of portal vein, VP, and 
hepatic veiu, vh; d t diaphragm; VC, vena cava; C, heart. 



SECRETION AND EXCRETION. 


125 


like the pancreas of Vertebrates in function, as its secre¬ 
tion digests starches and albuminoids. The liver of Ver¬ 
tebrates is both a secretory and an excretory organ. The 
bile performs an important, although ill-understood, func¬ 
tion in digestion, and also contains some waste products. 
The gland also serves to form sugar from part of the 
digested food, and may well be called a chemical work¬ 
shop for the body. In animals of slow respiration, as 
Crustaceans, Mollusks, Fishes, and Reptiles, fat accumu¬ 
lates in the liver. “Cod-liver oil” is an example. 

The great Excreting Organs are the lungs, the kid - 
neys , and the skin ; and the substances which they re¬ 
move from the system—carbonic acid, water, and urea— 
are the products of decomposition, or. organic matter on 
its way back to the mineral kingdom. 70 Different as these 
organs appear, they are constructed upon the same prin¬ 
ciple : each consisting of a very thin sheet of tissue sepa¬ 
rating the blood to be purified from the atmosphere, and 
straining out, as it were, the noxious matters. All, more¬ 
over, excrete the same substances, but in very different 
proportions: the lungs exhale carbon dioxide and water, 
with a trace of urea; the kidneys expel water, urea, and 
a little carbon dioxide; whil§ the skin partakes of the nat¬ 
ure of both, for it is not only respiratory, especially among 
the lower animals, but it performs part of the work of the 
kidneys when they are diseased. 

1. The lungs (and likewise gills) are mainly excretory 
organs. The oxygen they impart sweeps with the blood 
through every part of the body, and unites with the tis¬ 
sues and with some elements of the blood. Thus are pro¬ 
duced heat and work, whether muscular, nervous, secre¬ 
tory, etc. As a result of this oxidation, carbon dioxide, 
water, and urea or a similar substance, are poured into the 
blood. The carbon dioxide and part of the water are 
passed off from the respiratory organs. This process is 


126 


COMPARATIVE ZOOLOGY. 



more immediately necessary to life than any other: the 
arrest of respiration is fatal. 

2. While the lungs (and skin also, 
to a slight degree) are sources of 
gain as well as loss to the blood, the 
kidneys are purely excretory organs. 
Their main function is to eliminate 
the solid products of decay which 
cannot pass out by the lungs. In 
Mammals, they are discharged in 
solution; but from other animals 
which drink little the excretion is 
more or less solid. In Insects, the 
kidneys are groups of tubes; in the 

P.6. 93 .-sea.ou of Human lli g ll0r Mollusks, they are represent- 
Kidney, showing the tubu- e d by spongy masses of follicles; in 

lar portion, 3, grouped into 1 

cones; 7, the ureter, or out- Vertebrates, they are well-developed 
let of the secretion. i , •, j . , 

glands, two in number, and consist¬ 
ing of closely packed tubes. 

3. The skin of the soft-skinned animals, particularly of 
Amphibians and Mammals, is covered with minute pores, 
which are the ends of as many delicate tubes that lie 
coiled up into a knot within the true skin. These are 
the sweat-glands, which excrete water, and with it certain 
salts and gases. 

Besides these secretions and excretions, there are others, 
confined to particular animals, and designed for special 
purposes: such are the oily matters secreted from the 
skin of quadrupeds for lubricating the hair and keeping 
the skin flexible; the tears of Reptiles, Birds, and Mam¬ 
mals; the milk of Mammals; the ink of the Cuttle-fish; 
the poison of Jelly-fishes, Insects, and Snakes; and the 
silk of Spiders and Caterpillars. 



THE SKIN AND SKELETON. 


127 


CHAPTER XYI. 

THE SKIN AND SKELETON. 

The Skin, or Integument, is that layer of tissue which 
covers the outer surface of the body. The term Skeleton 
is applied to the hard parts of the body, whether external 
or internal, which serve as a framework or protection to 
the softer organs, and afford points of attachment to mus¬ 
cles. If external, as the crust of the Lobster, it is called 
Exoskeleton ; if internal, as the bones of Man, it is called 
Endoskeleton. The former is a modification of the skin; 
the latter, a hardening of the deeper tissues. 

1. The Skin.—In the lowest forms of life, as Amoeba, 
there is no skin. The jelly of which they are composed 
is firmer outside than inside, but no membrane is present. 
In Infusoria, there is a very thin cuticle covering the ani¬ 
mal. They have thus a definite form, while the Amoebae 
continually change. Sponges and Hydras also have no 
true skin. But in Polyps, the outside layer of the animal 
is separated into two portions—ecderon and enderon 71 — 
which may be regarded as partly equivalent to epidermis 
and dermis in the higher animals. These two layers are, 
then, generally present. The outer is cellular, the latter 
fibrous, and may contain muscular fibres, blood-vessels, 
nerves, touch-organs, and glands. It thus becomes very 
complicated in some animals. 

In Worms and Arthropods, the cellular layer, here 
called hypodermis, excretes a structureless cuticle, which 
may become very thick, as in the tail of the Horseshoe 
Crab, or may be hardened by deposition of lime-salts, as 
in many Crustacea. The loose skin, called the manile , 


128 


COMPARATIVE ZOOLOGY. 


which envelopes the body of the Mollusk corresponds tc 
the true skin of higher animals. The border of the man¬ 
tle is surrounded with a delicate fringe, and, moreover, 
contains minute glands, which secrete the shell and the 
coloring matter by which it is adorned. The Tunicates 
have a leathery epidermis, remarkable for containing, in¬ 
stead of lime, a substance resembling vegetable cellulose. 

In Mammals, whose skin is most fully developed, the 
dermis is a sheet of tough elastic tissue, consisting of in¬ 
terlacing fibres, and containing blood-vessels, lymphatics, 
sweat-glands, and nerves. It is the part converted into 
leather when hides are tanned, and attains the extreme 
thickness of three inches in the Rhinoceros. The upper 
surface in parts of the body is covered with a vast num¬ 
ber of minute projections, called papilla, each containing 
the termination of a nerve; these are the essential agents 
in the sense of touch. 72 They are best seen on the tongue 
of an Ox or Cat, and on the human fingers, where they 
are arranged in rows. 

Covering this sensitive layer, and accurately moulded 
to all its furrows and ridges, lies the bloodless and nerve¬ 
less epidermis. It is that part of the skin which is raised 
in a blister. It is thickest where there is most pressure 
or hard usage: on the back of the Camel it attains un¬ 
usual thickness. The lower portion of the epidermis 
(called rete mucosum) is comparatively soft, and consists 
of nucleated cells containing pigment-granules, on which 
the color of the animal depends. Towards the surface 
the cells become flattened, and finally, on the outside, are 
changed to horny scales (Fig. 2, c). 

These scales, in the higher animals, are constantly wear¬ 
ing off in the form of scurf, and as constantly being 
renewed from below. In Lizards and Serpents, the old 
epidermis is cast entire, being stripped off from the head 
to the tail; in the Toad, it comes off in two pieces; in the 


THE SKIN AND SKELETON. 


129 



B ig. 9«.—Section of Skin from Horse’s Nostril: E, epidermis; D, dermi-; 1, homy 
layer of epidermis; 2, rete mucosum; 3, papillary layer of dermis; 4, excretory 
duct of a sudoriparous, or sweat, gland; 5, glomerule, or convoluted tube of the 
same; 6, hair follicle ; 7, sebaceous gland; 8, internal sheath of the hair follicle; 
9, bulb of the hair; 10, mass of adipose tissue. 

Frog, in shreds; in Fishes and some Mollusks, in the form 
of slime. However modified the epidermis, or whatever 
its appendages, the like process of removal goes on. Mam¬ 
mals shed their hair; Birds, their feathers; and Crabs, 
their shells. When the loss is periodical, it is termed 
moulting. 

2. The Skeletons. — (l) The Exoskeleton is developed 
by the hardening of the skin, and, with very few excep¬ 
tions, is the only kind of skeleton possessed by inverte¬ 
brate animals. The usual forms are coral, shells, crusts, 
scales, plates, hairs, and feathers. It is horny or calca¬ 
reous; while the endoskeleton is generally a deposit of 
earthy material within the body, and is nearly confined 
to the Vertebrates. The exoskeleton may be of two kinds 
—dermal and epidermal. 

The microscopic particles of living jelly, called Polycis- 
tina and Foraminifera , possess siliceous and calcareous 
shells of the most beautiful patterns. The Sponge has a 

9 











130 


COMPARATIVE ZOOLOGY. 




skeleton of horny fibres, which is the sponge of commerce. 
Coral is the solid framework of certain Polyps. There 
are two kinds: one represented by the common white 
coral, which is a calcareous secretion within the body of 


Fig. 95.—1, Vertical Section, and, 2, Transverse Section, of a sclerodermic Corallite: 
a , mouth; b, tentacles; c, stomach; d, intermesenteric chamber; e, mesentery; 
/, septum; g , eudoderm; h, epitheca; k, theca, or outer wall; m, columella; «, 
short partitions; p, tabula, or transverse partition; r, sclerobase; a, ccenenchy- 
ma, or common substance connecting neighboring corallites; t, ectoderm; x, 
pali, or imperfect partitions. 


the Polyp, in the form of a cylinder, with partitions ra¬ 
diating towards a centre ( scleroderm ); the other, repre¬ 
sented by the solid red coral of jewelry, is a central axis 
deposited by a group of Polyps on the outside ( sclero¬ 
base ). The first 
sort is a dermal,the 
latter an epider¬ 
mal, exoskeleton. 

The skeleton of 
the Star-fish is a 
leathery skin stud¬ 
ded with calcare¬ 
ous particles and 
plates. The Sea- 
urchin is covered 
with an inflexible 

Fig. 96.— Shell of Sea-urchin {Cidaris) without, its spines. . 

shell oi elaborate 

and beautiful construction. The shell is really a calcified 



THE SKIN AND SKELETON. 


131 


skin, being a net-work of fibrous tissue and earthy matter. 
It varies in shape from a sphere to a disk, and consists 
of hundreds of angular pieces accurately fitted together, 
like mosaic-work. These form ten zones, like the ribs of 
a melon, five broad ones alternating with five narrower 



Fig. 97.—Structure of Sea-urchins’ Spines: 1, a, spine of Cidaris cut longitudinally; 
t, s, ball-and-socket joint; p, pedicellariae; 2,3, transverse sections of spines of 
Cidaris and Echinus. 

ones. The former (called interambulacra ) are covered 
with tubercles bearing movable spines. The narrow 
zones (called ambulacra , as they are likened to w r alks 
through a forest) are pierced with small holes, through 
which the animal sends out fleshy sucker-feet. 

The skin of the Crab and Lobster is hardened by cal¬ 
careous deposit into a “crust,” or shell; 73 but, instead of 
forming one piece, it is divided into a series of segments, 
which move on each other. The number of these seg¬ 
ments, or rings, is usually twenty-one—to the head, tho¬ 
rax, and abdomen, seven each. In the adult, however, 
the rings of the head and thorax are often soldered to¬ 
gether into one shield, called cembalo-thorax; and in the 
Horseshoe Crab the abdominal rings are also united. The 
shell of Crustaceans is periodically cast off, for the ani¬ 
mals continue to grow even after they have reached their 



132 


COMPARATIVE ZOOLOGY. 



mature form. This moulting is a very remarkable opera¬ 
tion. How the Lobster can draw its legs from their cases 

without unjointing 
or splitting them 
was long a puz¬ 
zle. The flesh be¬ 
comes soft, and is 
drawn through the 
joints, the wounds 
thus caused quickly 
healing. The cast¬ 
off skeleton is a per¬ 
fect copy of the an¬ 
imal, retaining in 
their places the del¬ 
icate coverings of 
the eyes and anten¬ 
nas, and even the 


Fig. 98.—Diagram of an Insect: A, head bearing the lining membrane of 
eyes and antennae; B, prothorax, carrying the first & 

pair of legs; C, mesothorax, carrying the second the Stomach with its 
pair of legs and first pair of wings; D, carrying the , 
third pair of legs and second pair of wings; E, ab- teetil. 
domen, with ovipositor, F; 1, coxa, or hip; 2, tro- rrn i 

chanter; 3, femur, or thigh; 4, tibia, or shank; 5, tar- 1 c uvi iiy Ub t 

sus, or foot; 6, claw. 0 f Insects differs 

from that of Crustaceans in consisting mainly of a horny 
substance called chitine and in containing no lime. The 
head, thorax, and abdomen are distinct, and usually con¬ 
sist of fourteen visible segments—one for the head, three 
for the thorax (called pvothorax , mesothorax , and metatho¬ 
rax ), and ten for the abdomen. The antennse, or feelers, 
legs, and wings, as well as hairs, spines, and scales, are ap¬ 
pendages of the skeleton. As Insects grow only during 
the larval, or caterpillar, state, moulting is confined to that 
period. These skeletons are epidermal, deposited in suc¬ 
cessive layers, from the inside, and are, therefore, capable 
of but slight enlargement when once formed. 





THE SKIN AND SKELETON. 


133 


The shells of Mollusks are well-known examples of exo¬ 
skeletons. The mantle, or loose skin, of these animals se¬ 
cretes calcareous earth in successive layers, converting the 
epidermis into a “shell.” 74 So various and characteristic 
is the microscopic character of shells, that a fragment is 
sometimes sufficient to determine the group to which it 
belongs. Many shells resemble that of the Fresh-water 
Mussel ( TJnio ), which is composed of three parts: the ex¬ 
ternal brown epidermis, of horny texture; then the pris¬ 
matic portion, consisting of minute columns set perpen¬ 
dicularly to the surface; and the internal nacreous layer, 
or “ mother-of-pearl,” made up of exceedingly thin plates. 
The pearly lustre of the last is due to light falling upon 
the outcropping edges of wavy laminae. 75 In many cases, 
the prismatic and nacreous layers are traversed by minute 
tubes. Another typical shell-structure is seen in the com¬ 
mon Cone, a section of which shows three layers, besides 
the epidermis, consisting of minute plates set at different 
angles. The Nautilus is composed of two distinct layers: 
the outer one having the fracture of broken china; the 
inner one, nacreous. 

Most living shells are made of one piece, as the Snail; 
these are called “ univalves.” Others, as the Clam, con¬ 
sist of two parts, and are called “ bivalves.” In either 
case, a valve may be regarded as a hollow cone, growing 
in a spiral form. The ribs, ridges, or spines on the out¬ 
side of a shell mark the successive periods of growth, and, 
therefore, correspond to the age of the animal. The 
figures on the following page show tke principal parts 
of the ordinary bivalves and univalves. The valves of a 
bivalve are generally equal, and the umbones, or beaks, a 
little in front of the centre. The valves are bound to¬ 
gether by a ligature near the umbones, and often, also, by 
means of a “ hinge ” formed by the “ teeth ” of one valve 
interlocking into cavities in the other. The aperture of 


COMPARATIVE ZOOLOGY. 


134 

a univalve is frequently closed by a horny or calcareous 
plate, called “ operculum,” which the animal carries on its 



Fig. 99. —Left Valve of a Bivalve Mollnsk (Cytherea Fig. 100. — Section of a Spiral 
chione ): h, hinge ligament; «, umbo; l, lunule; Univalve (Triton corrugatus): 

c, cardinal, and t, t\ lateral teeth; a, a', impres- a, apex; b, spire; c, suture; 

sions of the anterior and posterior adductor mus- d, posterior canal; e, outer 

cles; p, pallial impression ; *, sinus, occupied by lip of the aperture; /, ante- 

the retractor of the siphons. rior canal. 

only by the animal pouring out lime to cement the parts 
together. They cannot grow together, like a broken bone. 

Imbedded in the back of the Cuttle-fish is a very light 
spongy “ bone,” which, as already observed, is a secretion 
from the skin, and therefore belongs to the exoskeleton. 
It has no resemblance to true bone, but is formed, like 
shells, of a number of calcareous plates. Nevertheless, 
the Cuttle-fish does exhibit traces of an endoskeleton: 
these are plates of cartilage, one of which surrounds the 
brain, and hence may be called a skull. To this cartilage, 
not to the “ cuttle-bone,” the muscles are attached. 

In Vertebrates, the exoskeleton is subordinate to the 
endoskeleton, and is feebly developed in comparison. It 














THE SKIN AND SKELETON. 


135 



is represented by a great variety of appendages to the 
skin, which are mainly organs for protection, not for sup¬ 
port. Some are horny 
developments of the ep¬ 
idermis, such as hairs, 
feathers, nails, claws, 
hoofs, horns, and the 
scales of Reptiles; oth¬ 
ers arise from the hard¬ 
ening of the dermis by 
calcareous matter, as the 

scales of Fishes the hnnv FlG - 101 — Skeletal Architecture in the Armadil- 
in r isnes, me oon) l0j ghowil4 , the relation of the carapax to the 

plates of Crocodiles and vertebral column. 

Turtles, and the shield of the Armadillo. 

The scales of Fishes (and likewise the spines of their 
vertical fins) lie imbedded in the overlapping folds of the 
skin, and are covered with a thin, slimy epidermis. The 
scales of the bony Fishes (Perch, Salmon, etc.) consist of 



Fig. 102. —Diagrammatic Section of the Skin of a Fish (Carp): a , derm, showing lam¬ 
inated structure with vertical fibres, b ; c, gristly layer; e, laminated layer, with 
calcareous granules; d, superficial portion developing into scales; /, scale-pit. 

two layers, slightly calcareous, and marked by concentric 
and radiating lines. Those of the Shark have the structure 
of teeth, while the scutes, or plates, of the Crocodiles, 
Turtles, and Armadillos are of true bone. 

The scales of Snakes and Lizards are horny epidermal 
plates covering the overlapping folds of the true skin. 
In some Turtles these plates are of great size, and are 
called “ tortoise-shellthey cover the scutes. The scales 
on the legs of Birds, and on the tail of the Beaver and 
Rat, have the same structure. Hails are flattened horny 
plates developed from the upper surface of the fingers 










136 


COMPARATIVE ZOOLOGY. 



Fig. 103.—Vertical Section of the Forefoot of the Horse 
(middle digit): 1,2, 4, proximal, middle, and distal, 
or ungual, phalanges; 3, sesamoid, or nut-bone; 5, 
6, 7, tendons; 9, elastic tissue; 8, 10, internal and 
external floor of the hoof; 11,12, internal and exter¬ 
nal walls. 


and toes. Claws 
are sharp conical 
nails, being devel¬ 
oped from the sides 
as well as upper 
surface; and hoofs 
are blunt cylin¬ 
drical claws. Hol¬ 
low horns, as of the 
Ox, may be likened 
to claws sheathing 
a bony core. The 
horn of the Rhinoc¬ 
eros is a solid mass 
of epidermal fibres. 
“ Whalebone,” the 


rattles of the Rattlesnake, and the 
beaks of Turtles and Birds, are like¬ 
wise epidermal. 

Hairs, the characteristic clothing 
of Mammals, are elongated horny 
cones, composed of “pith” and 
“crust.” The latter is an outer 
layer of minute overlapping scales, 
which are directed towards the 
point, so that rubbing a human 
hair or fibre of wool between the 
thumb and finger pushes the root- 
end away. The root is bulbous, 
and is contained in a minute de¬ 
pression, or sac, formed by an in¬ 
folding of the skin. Hairs are usu¬ 
ally set obliquely into the skin. 
Porcupine’s quills and Hedgehog’s 
spines make an easy transition to 



Fig. 104.—Section oftheKootand 
part of the Shaft of a Human 
Hair; it is covered with epi¬ 
dermic scales, the inner layer, 
c, forming the outer covering 
of the shaft, being imbricated ; 
the root consists of angular 
cells loaded with pigment. 






THE SKIN AND SKELETON. 


137 


feathers, which differ from hairs only in splitting tip into 
numerous laminae. They are the most complicated of all 
the modifications of the epidermis. 

They consist of a “quill” (answer¬ 
ing to the bulb of a hair), and a 
“ shaft,” supporting the “ vane,” 
which is made up of “ barbs,” “ bar- 
bules,” and interlocking “process¬ 
es.” The quill alone is hollow, and 
has an orifice at each end. Thus 
feather is moulded on a papilla, the 
shaft lying in a groove on one side 
of it, and the vane wrapped around 
it. When the feather emerges from 
the skin, it unfolds itself. Thus 
shaft and vanes together resemble 
the quill split down one side and 
spread out. 

The teeth of Mollusks, Worms, 
and Arthropods are also epidermal 
structures. Those of Vertebrates are 
mixed in their origin, the dentine be- 
in £ derived from the dermis and the 
enamel from the epidermis. In all 
cases teeth belongto the exoskeleton. 

(2) The Endoskeleton, as we have 
seen, is represented in the Cuttle¬ 
fish. With this and some other 
exceptions, it is peculiar to Verte¬ 
brates. In the Cuttle-fish, and some Fishes, as the Stur¬ 
geon and Shark, it consists of cartilage; but in all others 
(when adult) it is bone or osseous tissue. Yet there is a 
diversity in the composition of bony skeletons; that of 
fresh-water Fishes contains the least earthy matter, and 
that of Birds the most. Hence the density and ivory- 



Fig. 105.—Parts of a Feather: 
a, quill, or barrel; b, shaft; c, 
vane, or beard; d, accessory 
plume, or down; e, /, lower 
and upper umbilicus, or ori¬ 
fice, leading to the interior 
of the quill. 





138 


COMPARATIVE ZOOLOGY. 


whiteness of the bones of the latter. Unlike the shells of 
Mollusks and the crust of the Lobster, which grow by the 
addition of layers to their borders, bones are moist, living 
parts, penetrated by blood-vessels and nerves, and covered 
with a tough membrane, called periosteum, for the attach¬ 
ment of muscles. 

The surface of bones is compact; but the interior may 
be solid or spongy (as the bones of Fishes, Turtles, Sloths, 
and Whales), or hollow (as the long bones of Birds and 
the active quadrupeds). There are also cavities (called 
“ sinuses ”) between the inner and outer walls of the skull, 
as is remarkably shown by the Elephant. The cavities in 
the long bones of quadrupeds are filled with marrow; 
those in the long bones of Birds and in skulls contain air. 

The number of bones not only differs in different ani¬ 
mals, but varies with the age of an individual. In very 
early life there are no bones at all; and ossification, or* 
the conversion of cartilage into bone, is not completed 
until maturity. This process begins at a multitude of 
points, and theoretically there are as many bones in a 
skeleton as centres of ossification. But the actual number 
is usually much less—a result of the tendency of these 
centres to coalesce. Thus, the thigh-bone in youth is 
composed of five distinct portions, which gradually unite. 
So in the lower Vertebrates many parts remain distinct 
which in the higher are joined into one. The occiput or 
back-bone of Man’s skull is the union of four bones, which 
are seen separate in the skull of the Fish, or of a baby. 

A complete skeleton, made up of all the pieces which 
might enter into its composition, does not exist. Every 
Vertebrate has some deficiency. All, except Amphioxus, 
have a skull and back-bone; but in the development of 
the various parts, and especially of the appendages, there 
is endless variety. Fishes possess a great number of skull- 
bone^ but have no fingers and toes. The Snake has plenty 


THE SKIN AND SKELETON. 


139 


of ribs and tail, but no breast-bone; the Frog has a breast¬ 
bone, but neither tail nor ribs. As the skeleton of a Fish 
i» too complicated for the primary student, we will select 
for illustration the skeleton of a Lion—the type of quad¬ 



rupeds. It should be remembered, however, that all Ver¬ 
tebrates are formed on one plan. 

In the lowest Vertebrate, Amphioxus, the only skeleton 
is a cartilaginous rod running from head to tail. There is 
no skull, nor ribs, nor limbs. In the cartilaginous Fishes, 











140 


COMPARATIVE ZOOLOGY. 


the backbone is only partially ossified. But usually it 
consists of a number of separate bones, called vertebra ar¬ 
ranged along the axis of the body. They range in number 
from 10 in the Frog to 305 in the Boa-constrictor. The 
skull, with its appendages, and the vertebrae, with the ribs 
and sternum, make up the axial skeleton. The shoulder 
and pelvic girdles and the skeleton of the limbs constitute 
the appendicular skeleton. 

A typical vertebra consists of a number of bony pieces 
so arranged as to form two arches, or hoops, connected by 


B. 




Fig. 107.—Vertebrae—A, cervical; B, dorsal; 2, centrnm; 4, transverse process, con¬ 
taining foramen, a, for artery; 5, articular process; 3, spinous process, or neural 
spine; 1, neural canal; 6, facets for head of rib, the tubercle of the rib fitting in 
a facet on the process, 4; b, laminae, or neurapophyses. 

a central bone, or centrum™ The upper hoop is called 
the neural arch , because it encircles the spinal marrow; 
the lower hoop is called the hcemal arch , because it en¬ 
closes the heart and the great central blood-vessels. An 
actual vertebra, however, is subject to so many modifica¬ 
tions, that it deviates more or less from this ideal type. 
Selecting one from the middle of the back: for an exam¬ 
ple, we see that the centrum sends off from its dorsal side 
two branches, or processes, called neurapophyses. These 
meet to form the neural arch, under which is the neural 
canal , and above which is a process called the neural 
spine. On the anterior and posterior edges of the arch 
are smooth surfaces, or zygapophyses , which in the natural 
state are covered with cartilage, and come in contact with 


THE SKIN AND SKELETON. 


141 


the corresponding surfaces of the preceding and succeed¬ 
ing vertebrae. The bases of the arch are notched in front 
and behind, so that when two vertebrae are put together a 
round opening {intervertebral foramen) appears between 
the pair, giving passage to the nerves issuing from the 
spinal cord. From the sides of the arch, blunt transverse 
processes project outward and backward, called diapophy¬ 
ses. Such are the main elements in a representative ver¬ 
tebra. The haemal arch is not formed by any part of the 
vertebra, but by the ribs and breast-bone. Theoretically, 
however, the ribs are considered as elongated processes 
from the centrum {pleurapophyses), and in a few cases a 
haemal spine is developed corresponding to the neural 
spine. 

The vertebrae are united together by ligaments, but 
chiefly by a very tough, dense, and elastic substance be¬ 
tween the centra. The neural arches form a continuous 
canal which contains and protects the spinal cord; hence 
the vertebral column is called the neuroskeleton. The 
column is always more or less curved; but the beautiful 
sigmoid curvature is peculiar to Man. The vertebrae 
gradually increase in size from the head towards the end 
of the trunk, and then diminish to the end of the tail. 
The neural arch and centrum are seldom wanting; the 
first vertebra in the neck has no centrum, and the last in 
the tail is all centrum. The vertebrae of the extremities 
(head and tail) depart most widely from the typical form. 

The vertebral column in Fishes and Snakes is divisible 
into three regions — head, trunk, and tail. But in the 
higher animals there are six kinds of vertebrae: cranial , 
cervical , dorsal , lumbar , sacral , and caudal. 

The cranial vertebra* form the skull. 77 They are greatly 
modified, as the neural arches are expanded to enclose the 
brain. The number of distinct bones composing the skull 
is greatest in Fishes, and least in Birds: this arises partly 


142 


COMPARATIVE ZOOLOGY. 



Fig. 110. 











THE SKIN AND SKELETON. 


143 


BONES OF THE MAMMALIAN SKULL* 

c 


BRAIN-CASE. . 


NASAL. 

LAC 

NOSE. 

ETHMOID. 


FRONTAL. 

HRYMAL. 

ORBITOSPHENOID. 

PRESPHENOID. 


PARIETAL. SUPRA OCCIPITAL. 

SQUAMOSAL. 

EYE. ALISPHENOID. PERI- EAR. OTIC. EXOCCIPITAL. 
MALAR. TYMPANIC. 

BASISPHENOID. BASIOCCIPITAL. 


VOMER. 

PREMAXILLA. MAXILLA. PALATINE. PTERYGOID. 
LOWER JAW, OR MANDIBLE. 


HYOID ARCH. 


THE SKULL OF THE DOG. 

Fig. 108.—Under surface. Fig. 109.—Upper surface. Fig. 110.— Lougitudiual ver¬ 
tical section; one-half natural size: SO, supraoccipital; ExO , exoccipital; BO, 
basioccipital; IP, interparietal; Pa, parietal; Fr, frontal; Sq, squamosal; Ma, 
malar; L, lachrymal; Mx, maxilla ; PMx, premaxilla ; Na, nasal; MT, maxillo- 
turbinal; ET, ethmoturbinal; ME, ossitied portion of the mesethmoid ; CE, cri¬ 
briform, or sieve-like, plate of the ethmoturbinal; VO, vomer; PS, presphenoid; 
OS, orbitosphenoid; AS, alispheuoid; BS, basisphenoid; PI, palatine; Pt, 
pterygoid ; Per, periotic ; Ty, tympanic bulla ; an, anterior narial aperture; ap, 
or apf, anterior palatine foramen; ppf posterior palatine foramen ; io, infra¬ 
orbital foramen; pof, postorbital process of frontal bone ; op, optic foramen ; sf, 
sphenoidal fissure ; fr, foramen rotundum, and anterior opening of alisphenoid 
canal; as, posterior opening of alisphenoid canal; fo, foramen ovale ; Jim, fora¬ 
men lacerum medium; of glenoid fossa; gp, postglenoid process; pgf, post¬ 
glenoid foramen ; earn, external auditory meatus; sm, stylomastoid foramen; 
flp, foramen lacerum posterius; cf condylar foramen ; pp, paroccipital process; 
oc, occipital condyle; fm, foramen magnum ; a, angular process ; s, symphysis of 
the mandible where it unites with the left ramus; id, inferior dental canal; cd, 
condyle; cp, coronoid process; the * indicates the part of the cranium to which 
the condyle is articulated when the mandible is in place; the upper border in 
which the teeth are implanted is called alveolar; sh, eh, ch, bh, th, hyoidean ap¬ 
paratus, or os linguae, supporting the tongue. In the skulls of old animals, 
there are three ridges: occipital, behind; sagittal, median, on the upper surface; 
and superorbital, across the frontal, in the region of the eyebrows. The last is 
highly developed in the Gorilla and other Apes. 


* In this diagram, modified from Huxley’s, the italicized bones are single; the 
rest are double. Those in the line of the Ethmoid form the Cranio -facial Axis: 
these, with the other sphenoids and occipitals, are developed in cartilage; the rest 
are membrane bones. In the Human skull, the four occipitals coalesce into one. 




144 


COMPARATIVE ZOOLOGY. 


from the fact that the bones remain separate in the for¬ 
mer case, while those of the chick become united together 
(anchylosed) in the full-grown Bird; but many bones are 
present in the Fish which have no representatives in the 
Bird. The skull consists of the brain-case and the face. 
The principal parts of the skull, as shown in the Dog’s, 
are: 1. The occipital bones behind,enclosing a large hole, 
ox foramen magnum , on each side of which are rounded 
prominences, called condyles , by which the skull articulates 
with the first cervical vertebra. 2. Th o parietal. 3. The 
frontal. These three form the main walls of the brain. 
4. The sphenoid , on the floor of the skull in front of the 
occipital, and consisting of six pieces. 5. The temporal , 
in which is situated the ear. In Man this is one bone; 
but in most animals there are three or more—th operiotic, 
tympanic , and squamosal. 6 . The malar , or “ cheek-bone,” 
which sends back a process to meet one from the squamo¬ 
sal, forming the zygomatic arch. 7. The nasal , or roof of 



Pig. 111. —Skull of the Horse: 1, premaxillary bone; 2, upper incisors; 3, upper 
canines; 4, superior maxillary; 5, infraorbital foramen; 6, superior maxillary 
spine; 7, nasal bones; 8, lachrymal; 9, orbital cavity; 10, lachrymal fossa; 11, 
malar; 12, upper molars; 13, frontal; 15, zygomatic arch; 16, parietal; 17, oc¬ 
cipital protuberance; 18, occipital crest; 19, occipital condyles; 20, styloid proc¬ 
esses; 21, petrous bone; 22, basilar process; 23, condyle of inferior maxillary; 
24, parietal crest; 25, inferior maxillary; 26, lower molars; 27, anterior maxillary 
foramen; 28, lower canines; 29, lower incisors. 


THE SKIN AND SKELETON. 


145 


the nose. 8. The maxilla / that part of the upper jaw in 
which the canines, premolars, and molars are lodged. 9. 
The premaxilla) in which the upper incisors are situated. 
10. The palatine , which, with the maxillary bones, forms 
the roof of the mouth. There are two appendages to the 
skull: the mandible , or lower jaw, whose condyles, or 
rounded extremities, fit into a cavity (the glenoid) in the 
temporal bone; and the hyoid , situated at the root of the 
tongue. 

The simplest form of the skull is a cartilaginous box, 
as in Sharks, enclosing the brain and supporting the car¬ 
tilaginous jaws and gill arches. In higher Fishes this box 
is overlaid with bony plates and partly ossified. In Frogs 
the skull is mainly bony, although a good deal of the car¬ 
tilage remains inside the bones. In higher Vertebrates the 
cartilage never makes an entire box, and early disappears. 

The cervical vertebrae, , or bones of the neck, are peculiar 
in having an orifice on each side of the centrum for the 
passage of an artery. The first, called atlas , because it 
supports the head, has no centrum, and turns on the sec¬ 
ond, called axis , around a blunt process, called the odon¬ 
toid. The centra are usually wider than deep, and the 
neural spines very short, except in the last one. The 
number of cervical vertebrae ranges from 1 in the Frog 
to 25 in the Swan. 

The dorsal vertebrae are such as bear ribs, which, uniting 
with the breast-bone, or sternum , form a bony arch over 
the heart and lungs, called the thorax. The sternum may 
be wanting, as in Fishes and Snakes, or greatly developed, 
as in Birds. When present, the first vertebra whose ribs 
are connected with it is the first dorsal. The neural spines 
of the dorsal series are generally long, pointing backward. 

The lumbar vertebrae are the massive vertebras lying in 
the loins between the dorsals and the hip-bones. 

The sacral vertebrae lie between the hip-bones, and are 
10 


146 


COMPARATIVE ZOOLOGY. 


generally consolidated into one complex bone, called so- 

crura. 

The caudal vertebrae, are placed behind the sacrum, and 
form the tail. They diminish in size, losing processes and 
neural arch, till finally nothing is left but the centrum. 
They number from 3 or 4 in Man to 270 in the Shark. 

Besides the lower jaw, hyoid, and ribs, Vertebrates 
have other appendages to the spinal column—two pairs 
of limbs.™ The fore limb is divided into the pectoral 
arch (or shoulder girdle ), the arm , and the hand. The 
arch is fastened to the ribs and vertebrae by powerful 
muscles, and consists of three bones, the scapula , or shoul¬ 
der-blade, the coracoid , and the clavicle , or collar-bone. 
The scapula and coracoid are generally united in Mam 
mals, the latter forming a process of the former; and the 
clavicles are frequently wanting, as in the hoofed animals. 
The humerus , radius , and ulna are the bones of the arm, 
the first articulating by ball-and-socket joint with the 
scapula, and by a hinge-joint with the radius and ulna. 
The humerus and radius are always present, but the ulna 
may be absent. The bones of the hand are divided into 
those of the carpus , or wrist; the metacarpus , or palm: 
and the phalanges , or fingers. The fingers, or “ digits,” 
range in number from 1 to 5. 

The hind limb is composed of the pelvic arch (or hip¬ 
bones), the leg , and the foot. These parts correspond 
closely with the skeleton of the fore limb. Like the 
shoulder, the pelvic arch, or os innominatum , consists of 
three bones— ilium , ischium , and pubis. The three are 
distinct in Amphibians, Beptiles, and in the young of 
higher animals; but in adult Birds and Mammals they 
become united together, and are also (except in Whales) 
solidly attached to the sacrum. The two pelvic arches 
and the sacrum thus soldered into one make the pelvis . 
The leg-bones consist of th q femur, or thigh; the tibia, or 


TIIE SKIN AND SKELETON. 


147 


shin-bone; and the fibula , or splint-bone. The rounded 
head of the femur tits into a cavity ( acetabulum ) in the 
pelvic arch, while the lower end articulates with the tibia, 
and sometimes (as in Birds) with the fibula also. An ex¬ 
tra bone, the patella, or knee-pan, is hung in a tendon in 
front of the joint between the femur and tibia of the high¬ 
er animals. The foot is made up of the tarsus , or ankle; 
the metatarsus , or lower instep; and the phalanges , or 
toes. The toes number from 1 in the Horse to 5 in Man. 

Certain parts of the skeleton, as of the skull, are firmly 
joined together by zigzag edges or by overlapping; in 
either case the joint is called a suture. But the great 
majority of the bones are intended to move one upon an¬ 
other. The vertebras are locked together by their proc¬ 
esses, and also by a tough fibrous substance between the 
centra, so that a slight motion only is allowed. The limbs 
furnish the best examples of movable articulations, as the 
ball-and-socket joint at the shoulder, and the hinge-joint 
at the elbow. The bones are held together by ligaments, 
and, to prevent friction, the extremities are covered with 
cartilage, which is constantly lubricated with an unctuous 
fluid called synovia. 


CHEMICAL COMPOSITION OF BONES. 



Cod. 

Tortoise. 

Hawk. 

Man. 

Phosphate of Lime, with trace of 





Fluate of Lime. 

57.29 

52.66 

64.39 

59.63 

Carbonate of Lime. 

4.90 

12.53 

7.03 

7.33 

Phosphate of Magnesia. 

2.40 

0.82 

0.94 

1.32 

Sulphate, Carbonate, and Chlorate 
of Soda. 

1.10 

0.90 

0.92 

0.69 

Glutine and Chondrine. 

32.31 

31.75 

25.73 

29.70 

Oil. 

2.00 

1.34 

0.99 

1.33 


100.00 

100.00 

100.00 

100.00 
















148 


COMPARATIVE ZOOLOGY, 


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Fig. 114. — Skeleton of the Whalebone Whale (Balcena mysticetus ), 


THE SKIN AND SKELETON 


149 



4 


I 


























150 


COMPARATIVE ZOOLOGY. 



Fig. 115.—Skeleton of the Tortoise (plastron removed): a, cervical vertebrae; c, dor¬ 
sal vertebrae; d, ribs; e, marginal bones of the carapace; l, scapula; k, precora¬ 
coid ; b, coracoid; /, pelvis; i, femur; g, tibia ; h, fibula. 



Fig. 116.—Skeleton of a Vulture: 1, cranium—the parts of which are separable only 
in the chick; 2, cervical vertebrae; 3, dorsal; 4, coccygeal, or caudal; the lumbar 
and sacral are consolidated; 5, ribs; 6, sternum, or breast-bone, extraordinarily 
developed; 7, furculum, clavicle, or “wish-bone;” S, coracoid; 9, scapula; 10, 
humerus; 11, ulna, with rudimentary radius; 12, metacarpals; 13, phalanges of 
the great digit of the wing; 19, thumb; 14, pelvis; 15, femur; 16, tibia-tar6us and 
fibula, or crus; 17, tarso-metatarsus; 18, internal digit, or toe, formed of three 
phalanges; the middle toe has four phalanges ; the outer, five; and the back toe, 
or thumb, two. 











THE SKIN AND SKELETON. 


151 



Fig. 117.— Skeleton of the Horse (Equus caballus) : 22, premaxillary: 12, foramen in 
the maxillary; 15, nasal; 9, orbit; 19, coronoid process of lower jaw ; 17, surface 
of implantation for the masseter muscle; there are seven cervical vertebrae, nine¬ 
teen dorsal, D-D; five lumbar, a-e; five sacral, f-l; and seventeen caudal, p-r; 
51, scapula, or shoulder-blade; i, spine, or crest; k, coracoid process (acromion 
wanting); 1, first pair of ribs (clavicle wanting, as in all Ungulates); e, sternum ; 
a , shaft of humerus; 6, deltoid ridge ; g, head fitting in the glenoid cavity of the 
scapula—near it is a great tuberosity for the attachment of a powerful muscle; 
k , condyles ; 54, radius, to which is firmly anchylosed a rudimentary ulna, 55, the 
olecranon ; 56, the seven bones of the carpus, or wrist; 57, large metacarpal, or 
“ cannon-bone,” with two “ splint-bones 58, fetlock-joint; 59, phalanges of the 
developed digit, corresponding to the third finger in Man; 62, pelvis; 63, the 
great trochanter, or prominence on the femur, 65; 66, tibia; 67, rudimentary 
fibula; 68, hock, or heel, falsely called knee; 69, metatarsals. 






















152 


COMPARATIVE ZOOLOGY. 



Fig. 118.— Skeleton of the Cow (Bos taurus). 



Fig. 119.—Skeleton of an Elephant (Elephac imacm) 

























THE SKIN AND SKELETON. 


153 













154 


COMPARATIVE ZOOLOGY. 


CHAPTER XYII. 

HOW ANIMALS MOVE. 

1. The power of animal motion is vested in protoplasm, 
cilia, and muscles. The power of contractility is one of 
the ultimate physiological properties of protoplasm, like 
sensibility and the power of assimilation. Protoplasma- 
animals, like the Amoeba and Rhizopoda, move by the 
contractility of their protoplasm, as also may the germs 
of higher animals upon the yolk of the egg. The proto¬ 
plasm may be extended into projections called pseudopodia, 
by whose contraction the animal may move (Fig. 186). 

Infusoria, and nearly all higher animals, possess cilia 
(Fig. 188). These are microscopic hairs (Fig. 2, b) which 
have the power of bending into a sickle-shape and straight¬ 
ening out. As they bend much faster than they straight¬ 
en, and as they all w r ork together, they can cause motion 
of the animal, or may serve to produce currents in the 
water, the animal remaining at rest. They are seen on 
the outside of Infusoria, and of very many embryos of 
higher animals, serving as paddles for locomotion; they 
fringe the gills of the Oyster, creating currents for respi¬ 
ration; and they line the passage to our lungs to expel 
the mucus. Flagella (Fig. 189) are a sort of long cilia, 
which are thrown into several curves when active, resem¬ 
bling a whip-lash, whence their name. Both cilia and fla¬ 
gella seem to be wanting in Arthropods. 

The cause of ciliary motion is unknown. Their one¬ 
sided contraction is their property, as the straight con¬ 
traction of the muscle-fibre belongs to it. Ho structure 
can, however, be seen in them with the microscope. Ho 


HOW ANIMALS MOVE. 


1 Ot) 

nerves go to them, yet they work in concert, waves of 
motion passing over a surface covered with cilia, as over 
a field of grain moved by the wind. 

But muscular tissue is the great motor agent, and exists 
in all animals from the Coral to Man. 79 The power of 
contractility, which in the Amoeba is diffused throughout 
the body, is here confined to bundles of highly elastic 
fibres, called muscles. When a muscle contracts, it tends 



Fig. 121.—A Contracting Muscle. 


to bring its two ends together, thus shortening itself, at 
the same time increasing in thickness. This shrinking 
property is excited by external stimulants, such as elec¬ 
tricity, acids, alkalies, sudden heat or cold, and even a 
sharp blow; but the ordinary cause of contraction is an 
influence from the brain conveyed by a nerve. The prop¬ 
erty, however, is independent of the nervous 
system, for the muscle may be directly stim¬ 
ulated. The amount of force with which a 
muscle contracts depends on the number of 
its fibres; and the amount of shortening, on 
their length. 

As a rule, muscles are white in cold-blooded 



animals, and red in the warm-blooded. They 
are white in all the Invertebrates, Fishes, n 
Batraehians, and Reptiles, except Salmon, V 
Sturgeon, and Shark; and red in Birds and ' 
Mammals, except in the breast of the com- F ' 8 <, trip 1 e 2 d 2 -Ma 9 U C a. 
■non fowl, and the like." _ “a Tt 

It is also a rule, with some exceptions, that nucleus, 
the voluntary muscles of Vertebrates, and all the muscles 






156 


COMPARATIVE ZOOLOGY. 


of the Lobster, Spider, and Insect tribes, are striated; while 
the involuntary muscles of Vertebrates, and all the muscles 
of Radiates, Worms, and Mollusks, are smooth. All mus¬ 
cles attached to internal bones, or to a jointed external 
skeleton, are striated. The voluntary muscles of Verte¬ 
brates are generally solid, and the involuntary hollow. 81 

This leads to another classification of muscles: into 
those which are attached to solid parts within the body; 
those which are attached to the skin or its modifications; 
and those having no attachments, being complete in them¬ 
selves. The last are hollow or circular muscles, enclosing 
a cavity or space, which they reduce by contraction. Ex¬ 
amples of such are seen in the heart, blood-vessels, stom¬ 
ach, iris of the eye, and around the mouth. In the lower 
Invertebrates, the muscular system is a net-work of longi¬ 
tudinal, transverse, and oblique fibres intimately blended 
with the skin, and not divisible into separate muscles. As 
in the walls of the human stomach, the fibres are usually 
in three distinct layers. This arrangement is exhibited by 
soft-bodied animals, like the Sea-anemone, the Snail, and 
the Earth-worm. Four thousand muscles have been count¬ 
ed in a Caterpillar. There are also “skin-muscles” in 
the higher animals, as those by which the Horse produces 
a twitching of the skin to shake otf insects, and those by 
which the hairs of the head and the feathers of Birds are 
made to stand on end. Invertebrates whose skin is hard¬ 
ened into a shell or crust have muscles attached to the 
inside of such a skeleton. Thus, the Oyster has a mass 
of parallel fibres connecting its two valves; while in the 
Lobster and Bee fibres go from ring to ring, both longi¬ 
tudinally and spirally. The muscles of all Invertebrates 
are straight parallel fibres, not in bundles, but distinct, 
and usually flat, thin, and soft. 

The great majority of the muscles of Vertebrates are 
attached to the bones, and such are voluntary. The fibres, 


HOW ANIMALS MOVE. 


157 


which are coarsest in Fishes (most of all in the Kays), and 
finest in Birds, are bound into bundles by connective tis¬ 
sue ; and the muscles thus made up are arranged in layers 
around the skeleton. Sometimes their extremities are at¬ 
tached to the bones (or rather to the periosteum) directly; 
but generally by means of white inelastic cords, called 
tendons. In Fishes, the chief masses of muscle are dis¬ 
posed along the sides of the bod} T , apparently in longitu¬ 
dinal bands, reaching from head to tail, but really in a 
series of vertical flakes, one for each vertebra. In propor¬ 
tion as limbs are developed, we find the muscles concen¬ 
trated about the shoulders and hips, as in quadrupeds. 
The bones of the limbs are used as levers in locomotion, 
the fulcrum being the end of a bone with which the mov¬ 
ing one is articulated. Thus, in raising the arm, the hu¬ 
merus is a lever working upon the scapula as a fulcrum. 
The most important muscles are called extensors flex¬ 
ors. The latter are such as bring a bone into an angle 
with its fulcrum—as in bending the arm—while the for¬ 
mer straighten the limb. Abductors draw a limb away 
from the middle line of the body, or a finger or toe away 
from the axis of the limb, while adductors bring them back. 

2. Locomotion.—All animals have the power of vol¬ 
untary motion, and all, at one time or another, have the 
means of moving themselves from place to place. Some 
are free in the embryo-life, and fixed when adult, as the 
Sponge, Coral, Crinoid, and Oyster. There may be no 
regular well-defined means of progression, as in the Amoe¬ 
ba, which extemporizes arms to creep over the surface; 
or movement may be accomplished by the contraction of 
the whole body, as in the Jelly-fish, which, pulsating about 
fifteen times in a minute, propels itself through the water. 
So the Worms and Snakes swim by the undulations of the 
body. 

But, as a rule, animals are provided with special organs 


158 


COMPARATIVE ZOOLOGY. 


for locomotion. These become reduced in number, and 
progressively perfected, as we advance in the scale of 
rank. Thus, the Infusorian is covered with thousands of 
hair-like cilia; the Star-iish has hundreds of soft, unjoint¬ 
ed, tubular suckers; the Centipede has from 30 to 40 
jointed hollow legs; the Lobster, 10; the Spider, 8; and 
the Insect, 6 ; the Quadruped has 4 solid limbs for loco¬ 
motion ; and Man, only 2. 

(1) Locomotion in Water.— As only the lower forms of 
life are aquatic, and as the weight of the body is partly 
sustained by the element, we must expect to find the or¬ 
gans of progression simple and feeble. The Infusoria 
swim with great rapidity by the incessant vibrations of 
the delicate filaments, or cilia, on their bodies. The com¬ 
mon Squid on our coast admits water into the interior of 
the body, and then suddenly forces it out through a fun¬ 
nel, and thus moves backward, or forward, or around, ac¬ 
cording as the funnel is turned—towards the head, or tail, 
or to one side. The Lobster has a fin at the end of its 
tail, and propels itself backward by a quick down-stroke 
of the abdomen. 

But Fishes, whose bodies offer the least resistance to 
progression through water, are the most perfect swimmers. 
Thus, the Salmon can go twenty miles an hour, and even 



Fig. 123—The Fins of a Fish (Pike-perch). 

ascend cataracts. They have fins of two kinds: those set 
obliquely to the body, and in pairs; and those which are 



HOW ANIMALS MOVE. 


159 



vertical, and single. The former, called pectoral and ven¬ 
tral fins, represent the fore and hind limbs of Quadrupeds. 
The vertical fins, which are only expansions of the skin, 
vary in number; but in most Fishes there are at least 
three: the caudal, or tail-fin; the dorsal, or back-fin; and 
the anal, situated on the abdomen, 
near the tail. The chief locomotive 
agent is the tail, which sculls like a 
stern-oar; the other fins are mainly 
used to balance and raise the body. 

When the two lobes of the tail are 
equal, and the vertebral column stops 
near its base, as in the Trout, it is said 
to be homocercal. If the vertebrae 
extend into the upper lobe, making 
it longer than the lower one, as in 
the Shark, the tail is called hetero- 
cercal. The latter is the more effec¬ 
tive for varying the course; the 
Shark, e. g., will accompany and 
gambol around a ship in full sail 
across the Atlantic. The Whale swims by striking the 
water up and down, instead of laterally, with a fin-like 
horizontal tail. Many air-breathing animals swim with 
facility on the surface, as the Water-birds, having webbed 
toes, and most of the Reptiles and Quadrupeds. 

(2) Locomotion in Air.— The power of flight requires a 
special modification of structure and an extraordinary 
muscular effort, for air is 800 times lighter than water. 
Nevertheless, the velocity attainable by certain Birds is 
greater than that of any Fish or Quadruped; the Hawk 
being able to go at the rate of 150 miles an hour. The 
bodies of Insects and Birds are made as light as possible 
by the distribution of air-sacs or air-cavities. 62 

The wings of Insects are generally four in number; 


Fig. 124.-Diagram illustrat¬ 
ing the locomotion of a 
Fish. The tail describes 
the arc of an ellipse; the 
resultant of the two im¬ 
pulses is the straight line 
in front 



160 


COMPARATIVE ZOOLOGY. 


sometimes only two, as in the Fly. They are moved by 
muscles lying inside the thorax. They are simple expan¬ 
sions of the skin, or crust, being composed of two delicate 
films of the epidermis stretched upon a net-work of tubes. 
There are three main varieties: thin and transparent, as 
in the Dragon-fly; opaque, and covered with minute col¬ 
ored scales, which are in reality flattened hairs, as in the 
Butterfly; and hard and opaque, as the 'first pair (called 
elytra) of the Beetle. 

The wings of Birds, on the other hand, are modified 
fore-limbs, consisting of three sets of feathers (called pri¬ 
mary , secondary , and tertiary ), inserted on the hand, fore¬ 
arm, and arm. The muscles which give the downward 
stroke of the wing are fastened to the breast-bone; and 
their power, in proportion to the weight of the Bird, is 
very great. Yet the Insect is even superior in vigor and 
velocity of flight. 83 In ascending, the Bird slightly rotates 
the wing, striking downward and a little backward; while 
the tail acts as a rudder. A short, rounded, concave wing, 
as in the common Fowl, is not so well fitted for high and 
prolonged flight as the long, broad, pointed, and flat wing 



Fig. 125.—Flamingoes taking Wing. 


of the Eagle. The wing is folded by means of an elastic 
skin and muscle connecting the shoulder and wrist. Be¬ 
sides Insects and Birds, a few other animals have the power 


HOW ANIMALS MOVE. 


161 


of flight, as Bats, by means of long-webbed fingers; Fly¬ 
ing Fishes, by large pectoral fins. Flying Reptiles, Flying 
Squirrels, and the like, have a membrane stretched on the 
long ribs, or connecting the fore and hind limbs, which they 
use as a parachute, enabling them to take very long leaps. 

(3) Locomotion on Solids. — This requires less muscular 
effort than swimming or flying. The more unyielding 
the basis of support, the greater the amount of force left 
to move the animal along. The simplest method is the 
suctorial, the animal attaching itself to some fixed object, 
and then, by contraction, dragging the body onward. But 
the higher and more common method is by the use of 
bones, or other hard parts, as levers. 

The Star-fish creeps by the working of hundreds of 
tubular suckers, which are extended by being filled with 



Fig. 126.—Diagrammatic section of Star-fish: a, mouth; b, stomach; e, hepatic cse- 
cum; d , dorsal or aboral surface; e, ambulacral plates; /, ovary; g , tubular feet; 
h , internal sacs for extending the feet 

fluid forced into them by little sacs. The Clam moves 
by fixing and contracting a muscular appendage, called 
a “foot.” The Snail has innumerable short muscles on 
the under side of its body, which, by successive contrac¬ 
tions, resembling minute undulations, enable the animal 
to glide forward apparently without effort. The Leech 
lias a sucker at each end: fixing itself by the one on its 
tail, and then stretching the body, by contracting the mus¬ 
cular fibres which run around it, the creature fastens its 
mouth by suction, and draws forward the hinder parts by 

11 






162 


COMPARATIVE ZOOLOGY. 


the contraction of longitudinal muscles. The Earth-worm 
lengthens and shortens itself in the same way as the Leech, 
but instead of suckers for holding its position, it has nu-| 
merous minute spines pointing backward; while the Cat-' 
erpillar has short legs for the same purpose. The legless 
Serpent moves by means of the scutes, or large scales, on 
the under side of the body, acted upon by the ribs. In 
a straight line, locomotion is slow; but by curving thej 
body, laterally or vertically, it can glide or leap with great 
rapidity. 

Most animals have movable jointed limbs, acted upon 
as levers by numerous muscles. The Centipede has forty- 

two legs, each with 
five joints and a claw. 
The Crab has five 
pairs of six-jointed 
legs; but the front 
pair is modified into 
pincers for prehen¬ 
sion. With the rest, 
which end in a sharp 
claw, the Crab moves 
backward, forward, 
or sideways. The 
Spider has eight legs, 
usually seven-joint¬ 
ed, and terminating 

Fig. 127. —Feet of Insects: A, Bibio febrilis; B, } n f wn 0 1 » W q fnntliml 
House-fly (Musca domestica ); C, Water - beetle 1 ° Clcl ^ S tOOtlied 

(Dytiscus). like a comb, and a 

third which acts like a thumb. In running, it moves the 
first right leg, then the fourth left; next, the first left, 
and then the fourth right; then the third right and sec¬ 
ond left together; and lastly, the third left and second 
right together. The front and hind pairs are, therefore,, 
moved like those of a quadruped. The Insect has six 



HOW ANIMALS MOVE. 


163 


legs, each of five parts: the coxa; trochanter; femur; 
tibia , or shank; and tarsus. The last is subdivided usu¬ 
ally into five joints and a pair of claws. Such as can 
walk upside down, as the Fly, have, in addition, two or 
three pads between the claws. 84 These pads bear hairs 
which secrete a sticky fluid, by means of which the Fly 
adheres to the surface. While the leg-bones of Verte¬ 
brates are covered by the muscles which move them, the 
limbs of Insects are hollow, and the muscles inside. The 
fore legs are directed forward, and the two hinder pairs 
backward. In motion, the fore and hind feet on one side, 
and the middle one on the other, are moved simultane¬ 
ously, and then the remaining three. 

The four-legged animals have essentially the same appa¬ 
ratus and method of motion. The Crocodile has an awk¬ 
ward gait, owing to the fact that the limbs are short, and 
placed far apart, so that the muscles act at a mechanical dis¬ 
advantage. The Tortoise is proverbially slow,for a similar 
reason. Both swim better than they w T alk. Lizards are light 
and agile,but progression is aided by a wriggling of the body. 

The locomotive organs of the mammalian quadrupeds 
are much more highly organized. The bones are more 
compact; the vertebral column is arched, and yet elastic, 
between the shoulder and hip, and the limbs are placed 
vertically underneath the body. The bones of the fore 
limb are nearly in a line; but those of the hind limb, 
which is mainly used to project the body forward, are 
more or less inclined to one another, the angle being most 
marked in animals of great speed, as the Horse. Some 
walk on hoofs, as the Ox (Ungulate); some on the toes, 
as the Cat (Digitigrade); others on the sole, touching the 
ground with the heel, as the Bear (Plantigrade). In the 
Pinnigrade Seal, half of the fore limb is buried under the 
skin, and the hind limbs are turned backward to form a 
fin with the tail. The normal number of toes is five; but 


164 


COMPARATIVE ZOOLOGY. 



Fig. 128.—Feet of Carnivores : A, Plantigrade {Bear); B, Pinuigrade {Seal): C, 

Digitigrade {Lion). 


some may be wanting, so that we have one-toed animals 
(as Horse), two-toed (as Ox), three-toed (as Rhinoceros), 
four-toed (as Hippopotamus), and five-toed (as the Ele¬ 
phant). The Horse steps on what corresponds to the nail 
of the middle finger; and its swiftness is conditioned on 
the solidity of the extremities of the limbs. Horses of 
the greatest speed have the shoulder-joints directed at a 
considerable angle with the arm. 



Fig. 12£*. Feet of Hoofed Mammals: A, Elephant; B, Hippopotamus; C, Tthinoc- 
eros; I), Ox; E, Horse, a, astragalus; cl, calcaneum, or heel; s, naviculare; b, 
cuboides; ce, ci, cm, cuneiform bones; the numbers indicate the digits in use. 










HOW ANIMALS MOVE. 


165 


The order in which the legs of Quadrupeds succeed 
each other determines the various modes of progression, 
called the walk, trot, gallop, and leap. Many, as the 
Horse, have all these movements; while some only leap, 
as the Frog and Kangaroo. In leaping animals, the hind 
limbs are extraordinarily developed. In many Mammals, 
like the Squirrel, Cat, and Hog, the fore legs are used for 
prehension as well as locomotion. Monkeys use all four, 



Fig. 130. — Muecles of the Human Leg: 
sartorius , or “tailor’s muscle,” the 
longest muscle in the body, flexes the 
leg upon the thigh; rectus femoris 
and vastus externus and interims ex¬ 
tend the leg, maintaining an erect 
posture; gastrocnemius , or “calf,” 
used chiefly in walking, for raising 
the heel. Another layer underlies 
these superficial muscles. 



Fig. 131. — Muscles of an Insect’s Leg 
(Melolontha vulgaris ): a, flexor, and 
b, extensor, of tibia; c, flexor of foot; 
d, accessory muscle; e, extensor of 
claw; /, extensor of tarsus. The 
joints are restricted to movements 
in one plane; and therefore the mus¬ 
cles are simply flexors and extensors. 
All the muscles are within the skele¬ 
ton. 




166 


COMPARATIVE ZOOLOGY. 


and also the tail, for locomotion and prehension, keeping 
a horizontal attitude; while the Apes, half erect, as if 
they were half-quadruped, half-biped, go shambling along, 
touching the ground with the knuckles of one hand and 
then of the other. In descending the scale, from the 
most anthropoid Ape to the true Quadruped, we find the 
centre of gravity placed increasingly higher up—that is, 
farther forward. Birds and Men are tbe only true bipeds ; 
the former standing on their toes, the latter on the soles 
of the feet. Terrestrial Birds walk and run ; while Birds 
of flight usually hop. The Ostrich can for a time outrun 
the Arabian Horse; and the speed of the Cassowary ex¬ 
ceeds that of the swiftest Greyhound. 


CHAPTER, XVIII. 

THE NERVOUS SYSTEM. 


Nervous Matter exists in the form of cells, fibres, or 

tubes. In the cellular state it is grayish, and accumulated 

b in masses, called 

ganglia , or centres , 

which alone origi- 
© 

nate nervous force; 
the fibrous and tu¬ 
bular kinds are gen¬ 
erally white, and 
arranged in bun¬ 
dles, called nerves , 
which serve only as 
conductors. Most 
nerves contain two 
kinds of fibres, like 
in structure, but 



Fig. 132. — Nerve-cells from Human Brain: A, associ¬ 
ated with nerve-tubes and blood-vessels; B, multi¬ 
polar nucleated cells. 






THE NERVOUS SYSTEM. 


167 



Fig. 183. —Nervous System of Star¬ 
fish: Diagram — r, nervous ring 
around mouth; n, radial nerves to 
each arm, ending in the eye. 


each having its distinct office: one carries impressions re¬ 
ceived from the external world to the gray centres, and 
lienee is called an afferent, or sen¬ 
sory , nerve; the other conducts 
an influence generated in the 
centre to the muscles, in obedi¬ 
ence to which they contract, and 
hence it is called an efferent , or 
motor , nerve. Thus, when the 
finger is pricked with a pin, af¬ 
ferent nerve-fibres convey the 
impression to the centre—-the 
spinal cord, which immediately 
transmits an order by efferent fibres to the muscles of the 
hand to contract. If the former are cut, sensation is lost, 
but voluntary motion remains ; if the latter are cut, the 
animal loses all control over the muscles, although sensi¬ 
bility is perfect; if both are cut, the animal is said to be 
paralyzed. The nerve-fibres are 
connected with nerve-cells in the 
central organs, and at the outer 
ends are connected with the mus¬ 
cular fibres, or with various sen¬ 
sory end-organs in the skin or 
other parts of the body. The 
nature of nerve-force is not 
known. As to the velocity of a 
nervous impulse, we know it is 
far less than that of electricity or 
light, and that it is more rapid in 

iriG. 184 .-Nervous System of a warm-blooded than in sold-blood- 

Moiiusk (the Gasteropod Apiys- e( j animals, being faster in Man 
ia): a, anterior ganglion; c, ce- # ° 

phaiic? i, lateral; g, abdominal, than in the Frog. In the latter 
it averages about 85 feet per second, in the former over 
100 feet. 





168 


COMPARATIVE ZOOLOGY. 



The very lowest animals, like the Amoeba and Infuso¬ 
ria, have no nerves, although their protoplasm has a gen¬ 
eral sensibility. The Hydra has certain 
cells which are, perhaps, partly nervous 
and partly muscular in function. The 
Jelly-fish has a nervous system, consist¬ 
ing of a net-work of threads and ganglia 
scattered all over its disk. We should 
look for a definite system of ganglia and 
nerves only in those animals which pos¬ 
sess a definite muscular structure, and 
show definitely co-ordinat¬ 
ed muscular movements. 

In the Star-fish we detect 
the first clear specimen of 
such a system. It consists 

Fig. 135.— Nervous Sys- Q f a r i n g ai’OUnd the mouth, 
tem of Clam: c, cere- 0 , 

braiganglion?p,ped- made of five ganglia 01 

tosptaochnicganglia; equal size, with radiating 

nerves. The Mollusks are 

from cerebral to pedal distinguished by an irregu- 
ganglia ; ps', commis- ° ^ ° 

sure from cerebral to larly scattered nervous S} T S- 
parietosplanchnic . /-ni i .i 

ganglia; oe, cesopha- tem. The Clam lias three 

gus * main pairs of connected 

ganglia—one near the mouth, one in the 

foot, and the third in the posterior region, 

near the siphons. In the Snail, these are 

united into a ring around the gullet, and 

there are other ganglia scattered through 

the body. The same is true of the Cuttle- Fig. m—Nervous 

fish, where the brain is partly enclosed in a 

cartilaginous box (Fig. 151). 

In the simpler worms there is but a sin- head > ganglion, 
gle ganglion or a single pair. The Earth-worm has a pair 
of brain-ganglia lying above the gullet, and connected by 






THE NERVOUS SYSTEM. 


169 


two cords witli a ventral chain of ganglia—one pair, ap¬ 
parently a single one, for each segment. In the lower 
Arthropods, snch as Crustacea, Centipedes, and Larval In¬ 
sects, the arrangement is substan¬ 
tially the same. In higher Insects 
and Crustacea, many of the gan¬ 
glia are fused together in the head 
and thorax, indicating a concen¬ 
tration of organs for sensation and 
locomotion. 

In Yertebrates, the nervous 
system is more highly developed, 
more complex, and more concen¬ 
trated than in the lower forms. 

In fact, there are some parts, as the 
brain, to which we find nothing: 
homologous in the Invertebrates; 
and while the actions of the lat¬ 
ter are mainly, if not wholly, au¬ 
tomatic, those of backboned ani¬ 
mals are voluntary. Its position, 
moreover, is peculiar, the great 
mass of the nervous matter being 
accumulated on the dorsal side, 
and enclosed by the neural arches 
of the skeleton. 

The brain and spinal cord lie 
in the cavity of the skull and 
spinal column, wrapped in three 
membranes. Both consist of gray 
and white nervous matter; but in 
the brain the gray is on the out¬ 
side, and the white within; while 
the white of the spinal cord is external, and the gray in¬ 
ternal. Both are double, a deep fissure running from the 



Fig. 137.—Human Brain and Spinal 
Cord, one fifth natural size: a, 
great longitudinal fissure; b, an¬ 
terior lobe; c, middle lobe; d, 
medulla oblongata; e, cerebel¬ 
lum; /.first spinal nerve; g, 
brachial plexus of nerves supply¬ 
ing the arms; h , dorsal nerves; i, 
lumbar nerves; k, sacral plexus 
of nerves for the limbs; l, canda 
equina: the figures indicate the 
twelve pairs of cranial nerves, of 
which 1 is olfactory, 2 optic, and 
8 auditory. 








170 


COMPARATIVE ZOOLOGY. 


forehead backward, dividing the brain into two hemi¬ 
spheres, and the spinal cord resembling two columns 
welded together; even the nerves come forth in pairs to 
the right and left. The brain is the organ of sensation 
and voluntary motion; the spinal cord is the organ of in¬ 
voluntary life and motion. The brain, above the medulla 
oblongata, may be removed, and yet the animal, though it 
cannot feel, will live for a time, showing that it is not ab¬ 
solutely essential to life; in fact, the brain does nothing 
in apoplexy and deep sleep. All of the cord, except that 
part containing the centres for respiration and circulation, 
may also be destroyed, without causing immediate death. 

The Brain is that part of the nervous system contained 
in the skull. 86 It increases in size and complexity as we 
pass from the Fishes, by the Amphibians, Reptiles, and 
Birds, to Mammals. Thus, the body of the Cod is 5000 
times heavier than its brain—in fact, the brain weighs less 
than the spinal cord; while in Man, the brain, compared 
with the body, is as 1 to 36, and is 40 times heavier than 
the spinal cord. The brains of the Cat weigh only 1 oz.; 
of the Dog, 6 oz. dr.; and of the Horse, 22 oz. 15 dr. 
The only animals whose brains outweigh Man’s are the 
Elephant and Whale—the maximum weight of the Ele¬ 
phant’s being 10 lbs., and of the Whale’s 5 lbs.; while 
the human does not exceed 4 lbs. Yet the human brain 
is heavier in proportion to the body. But quality must 
be considered as 'well as quantity, else the Donkey will 
outrank the Horse, and the Canary-bird, Man; for their 
brains are relatively heavier. 

The main parts of the brain are the cerebrum , cerebel¬ 
lum, and medulla oblongata . 

The cerebrum is a mass of white fibrous matter covered 
by a layer of gray cellular matter. In the lower Verte¬ 
brates, the exterior is smooth; but in most of the Mam¬ 
mals it is convoluted, or folded, to increase the amount of 


THE NERVOUS SYSTEM. 


171 



the gray surface. The convolutions multiply and deepen 
as e ascend the scale of size and intelligence, being very 
complex in the Elephant and Whale, Monkey and Man. 
As a rule, they are proportioned to the intelligence of the 
animal; yet the brains 
of the Dog and Horse 
are smoother than those 
of the Sheep and Don¬ 
key. Evidently the 
quality of the gray mat¬ 
ter must be taken into 
account. Save in the 
bony Fishes, the cere¬ 
brum is the largest por¬ 
tion of the brain ; in 
Man it is over eight 
times heavier than the 
cerebellum. 

The cerebellum, or 
“ little brain,” lies be¬ 
hind the cerebrum, and, 
like it, presents an ex¬ 
ternal gray layer, with 
a white interior. In 
Mammals, it is likewise 
finely convoluted, con¬ 
sisting of gray 
white laminae, and is 
divided into two lobes, 
or hemispheres. In the rest of the Vertebrates, the cere¬ 
bellum is nearly or quite smooth; and in the lowest Fish¬ 
es it is merely a thin plate of nervous matter. In many 
Vertebrates, however, it is larger, compared with the cere¬ 
brum, than in Man, since in Man the cerebrum is extraor¬ 
dinarily developed. 


1 Fig. 138. —Brain of the Horse—npper view, one 
d 1 half natural size: a, medulla oblongata; 6, lat¬ 
eral and middle lobes of cerebellum; c, inter¬ 
lobular fissure; d, cerebral hemispheres; e, ol¬ 
factory lobes. 



172 


COMPARATIVE ZOOLOGY. 


The medulla oblongata is the connecting link between 
the cerebrum and cerebellum and the spinal cord. In 
structure, it resembles the spinal cord—the white matter 
being external and the gray internal. The former lies 
beneath or behind the brain, passing through the foramen 
magnum of the skull, and merging imperceptibly into the 
cord. The latter is a continuous tract of gray matter en¬ 
closed within strands of white fibres. It usually ends in 
the lumbar region of the vertebral column, but in Fishes 
it reaches to the end of the tail. In Fishes, Amphibians, 
and Reptiles, the cord outweighs the brain: in Birds and 
Mammals, the brain is heavier than the cord. In Man, 
it weighs about an ounce and a half. 

Besides these parts, there are also the olfactory and the 
optic lobes, which give rise respectively to the nerves of 
smell and sight. 

The parts of the brain are always in pairs; but in rela¬ 
tive development and po¬ 
sition they differ widely in 
the several classes of Ver¬ 
tebrates. In Fishes and 
Reptiles, they are arranged 
in a horizontal line; in 
Birds and Mammals, the 
axis of the spinal cord 
bends to nearly a right an- 

F, the 3 p e 7cb,'"upper S le in P assin S through the 

view: a, cerebei- brain, so that the lobes no 

Jura; b, optic . , 

lobes; c, cere- longer he in a straight line. 

brnm; i, olfacto- t T\r , x .... 

ry lobes; g, me- Alan, tile IOre-bl’ain is Fig. 140.—Brain of the 

Frog, upper view, x 4: 
/.olfactorynerves; Lol, 
olfactory lobes; He, cer- 




duiia oblongata. so developed that it cov. 
ers all the other lobes. In looking down 
upon the brain of a Perch, we see in 
front a pair of olfactory lobes (which 
send forth the nerves of smell), behind 


ebral hemispheres; Pn , 
pineal gland; Fho and 
Srh, third and fourth 
ventricles; Lop , optic 
lobes; C, cerebellum; 
Mo, medulla oblongata. 


THE NERVOUS SYSTEM. 


173 


them the small cerebral hemispheres, then the large optic 
lobes (in which originate the nerves of sight), and, last of 
all, the cerebellum. Not till we reach Man and the Apes 
do we find the cerebrum so highly developed as to overlap 
both the olfactory lobes in front and the cerebellum behind. 

Functions of the Brain.— The cerebrum is the seat of in¬ 
telligence and will. It has no direct communication with 
the outside world, receiving its consciousness of external 
objects and events through the spinal cord and the nerves 
of special sense. 86 

The cerebellum seems to preside over the co-ordination 
of the muscular movements. When removed, the animal 



Fra. 141.—A. C, npper and aide views of the Brain of a Lizard; B, D, upper and side 
views of the Brain of a Turkey: Olf, olfactory lobes; Hmp, cerebral hemispheres; 
Pn, pineal gland ; Mb, optic lobes of the middle brain; Cb, cerebellum; MO, me¬ 
dulla oblongata; ii, optic nerves; iv and vi, nerves for the muscles of the eye: 
Py, pituitary body. 

desires to execute the mandates of the will, but cannot; 
its motions are irregular, and it acts as if intoxicated. It 
is usually largest in animals capable of the most compli- 
cated movements; being larger in the Ape than in the 
Lion, in the Lion than in the Ox, in Birds than in Rep¬ 
tiles. The cerebellum of the Frog is, however, smaller 
than that of Fishes (Figs. 139,140). The olfactory and op< 
tic lobes receive the messages from their respective nerves. 


174 


COMPARATIVE ZOOLOGY. 


The medulla oblongata is not only the medium of com¬ 
munication between the brain and the spinal cord, but it 



Fig. 142.— Brain of the Cat (Felis do- 
mestica): a, medulla oblongata; b, 
cerebellum; c, cerebrum. 



Fig. 143. —Brain of the Orang-utan, 
upper surface; one third natural 
size. 



is itself a nervous centre: the brain above and the cord 
below may be removed without death to the animal, but 
the destruction of the medulla is fatal. Of the twelve 
pairs of nerves issuing from the contents of the skull (en¬ 
cephalon), ten come from the 
medulla oblongata. Among 
these are the nerves of hearing 


Fig. 144.—Human Brain, side view: 1, 
medulla oblongata; 3, cerebellum ; 5, 
frontal convolutions of cerebrum. 


Fig. 145. — Human Brain, upper v.evv, 
one third natural size: 1, anterior 
lobes ; 2, posterior; 3, great mediau 
fissure. 


and taste, and those that control the lungs and heart. Ees- 
piration ceases immediately when the medulla is injured. 




THE NERVOUS SYSTEM. 


175 


The spinal cord is a centre for originating involuntary 
actions, and is also a conductor—propagating through its 
central gray matter the impressions received by the nerves 
to the brain, and taking back through its fibrous part the 
impulses of the brain. r 

In Man, thirty-one pairs 
of nerves arise from the 
cord to supply the whole 
body, except the head. 

Each nerve has an ante¬ 
rior and a posterior root. 

The fibres of the former 
go to the muscles, and 
hence carry the impulses 
which cause muscular 
contraction (hence call¬ 
ed motor fibres ); those 
of the posterior root con- 
ve} T sensations from the 
exterior to the central 
organs (sensory). The 
fibres leading from the 
brain to the cord cross 

nnp a noth or in the me- Fia ’ 146 — Relation of the Sympathetic and Spinal 
one anotnei ill me me Nerves: c, Assure of spiual cord; a, anterior of 

dulla oblongata, SO that a dorsal s P inal nerve : posterior root, with its 
° 7 ganglion; a', anterior branch; p', posterior 

if the right cerebral branch; s, sympathetic; e, its double junction 
. . it , by white and gray filaments. 

hemisphere be diseased, 

the left side of the body loses the power of voluntary 



motion. 

The sympathetic nervous system is a double chain of 
ganglia, lying along the sides of the vertebral column in 
the ventral cavity. From these ganglia nerves are given 
off, which, instead of going to the skin and muscles, like the 
spinal nerves, form net-works about those internal organs 
over which the will has no control, as the heart, stomach, 










176 


COMPARATIVE ZOOLOGY. 


and intestines. Their apparent office is to stimulate these 
organs to constant activity, but is little understood. 

1. The Senses. 

Sensation is the consciousness of impressions on the 
sensory nerves. These impressions produce some change 
in the brain; but what that change is, is a darkness on 
which no hypothesis throws light. Obviously, we feel 
only the condition of our nervous system, not the objects 
which excite that condition . 87 

All animals possess a general sensibility diffused over 
the greater part of the body . 88 This sensibility, like as¬ 
similation and contractility, is one of the primary physio¬ 
logical properties of protoplasm. But, besides this (save 
in the very lowest forms), they are endowed with special 
nerves for receiving the impressions of light, sound, etc. 
These nerves of sense, as they are called, although struct¬ 
urally alike, transmit different sensations: thus, the Ear can¬ 
not recognize light, and the Eye cannot distinguish sounds. 
In the Vertebrates, the organs of sight, hearing, and smell 
are situated in pairs on each side of the head; that of 
taste, in the mucous membrane covering the tongue; 
while the sense of touch is diffused over the skin. Sight 
and hearing are stimulated, each by one agent only; 
while touch, taste, and smell may be excited by various 
substances. The agents awakening sight, hearing, and 
touch are physical; those causing taste and smell are 
chemical. Animals differ widely in the numbers and 
keenness of their senses. But there is no sense in any 
one which does not exist in some other. 

Touch is the simplest and the most general sense; no an¬ 
imal is without it, at least in the form of general sensibility. 
It is likewise the most positive and certain of the senses. 
In the Sea-anemone, Snail, and Insect, it is most acute in 
the “feelers’’ (tentacles, horns, and antennae ), 89 in the Oys- 


THE NERVOUS SYSTEM. 


177 


ter, the edge of the mantle is most sensitive; in Fishes, 
the lips; in Snakes, the tongue; in Birds, the beak and 
under side of the toes; in 
Quadrupeds, the lips and 
tongue; and in Monkeys 
and Man, the lips and the 
tips of the tongue and fin¬ 
gers. In the most sensitive 
parts of Birds and Mam¬ 
mals, the true skin is raised 
up into multitudes of mi¬ 
nute elevations, called jpa- 
piUce^ containing loops of 
capillaries and nerve-filaments. There is a correspondence 
between the delicacy of touch and the development of in¬ 
telligence. The Cat and Dog are more sagacious than 
hoofed animals. The Elephant and Parrot are remark¬ 
ably intelligent, and are as celebrated for their tactual 
power. 

Taste is more refined than touch, since it gives a 
knowledge of properties which cannot be felt. It is al¬ 
ways placed at the entrance to the digestive canal, as its 
chief purpose is to guide animals in their choice of food. 

]STo special organ of taste can be de¬ 
tected in the Invertebrates, although 
all seem to exercise a faculty in se¬ 
lecting their food. Even in Fishes, 
Amphibians, Reptiles, and Birds this 

Fig. 148.—Papillae of Human x , 

Palm, x 35 , the cuticle be- sense is very obtuse, for they bolt 
mg removed. their food. But the higher Verte¬ 

brates have it well developed. It is confined to the 
tongue, and is most delicate at the root . 90 A state of 
solution and an actual contact of the fluid are necessary 
conditions. 

Smell is the perception of odors, i. e ., certain substances 
12 




Fig. 147.—Antennae of Various Insects. 



COMPARATIVE ZOOLOGY. 


178 

in the gaseous state. Many Invertebrates have this sense: 
Snails, e. g ., seem to be guided to their food by its scent, 
and Flies soon find a piece of meat. In the latter the 
organ is probably located on the antennae. In Verte¬ 
brates, it is placed at the entrance 
to the respiratory tube, in the upper 
region of the nose. There the olfac- 
tory nerves, which issue from the olfac¬ 
tory lobe of the brain, and pass through 
the ethmoid bone, or roof of the nasal 
F on\t“ w “L N r s “ cavity, are distributed over a moist 
cavity. mucous membrane. The odorous sub¬ 

stance, in a gaseous or finely divided state, is dissolved in 
the mucus covering this membrane. In Fishes and Rep¬ 
tiles generally, this organ is feebly developed; Sharks, 
however, gather from a great distance around a carcass. 
In the Porpoises and Whales it is nearly or entirely 
wanting. Among Birds, Waders have the largest olfac¬ 
tory nerves. It is most acute in the carnivorous Quad¬ 
rupeds, and in some w T ild herbivores, as the Deer. In 
Man it is less delicate, but has a wider range than in any 
brute. 

Hearing is the perception of sound. The simplest 
form of the organ is a sac filled with fluid, in which float 
the soft and delicate ends of the auditory nerve. The 
vibrations of the fluid are usually strengthened by the 
presence of minute hard granules, call¬ 
ed otoliths. Most Invertebrates have 
no higher apparatus than this; and it 
is probable that they can distinguish 
one noise from another, but neither 

. Fig. 150—Ear of a Mol- 

pitch nor intensity. I he organ is gen- lusk (Oycias), greatly en- 
erally double, but not always located larged ’ 
in the head. In the Clam, it is found at the base of the 
foot; some Grasshoppers have it in the fore-legs; and in 





THE NERVOUS SYSTEM. 


179 


many Insects it is on the wing. Lobsters and Crabs have 
the auditory sacs at the base of the antennae. 91 



Fig. 151 _Brain and Auditory Apparatus of the Cuttle-fish: a, b, brain; c, auditory 

apparatus; d, the cavity iu which it is lodged; e,f, g , eyes; 1,2,3, otoliths. 



A complex organ of hearing, located in the head, exists 
in all Vertebrates, save the very lowest Fishes. As com¬ 
plete in Man, it consists of the following parts: 1st. The 
external ear (which is peculiar to Mammals); the auditory 
canal, about an inch long, lined with hairs and a waxy se¬ 
cretion, and closed at the 
bottom by a membrane, 
called t y mp a mom, or 
“drum of the ear.” 2d. 

The middle ear, contain¬ 
ing three little bones (the 
smallest in the body), mal¬ 
leus , incus , and stapes, ar¬ 
ticulated together. The 

cavity communicates with Fig. 152.—Section of Human Ear: a, external 
J . ear > w i th auditory canal; 6, tympanic cavi- 

the external air by means ty containing the three bones; c, hammer, 
-c and its three muscles, d, e,f; g, tympanic 

OX tne iliUStacnian tuoe, membrane, or head of the drum; h, Eusta- 


Tjrln’pb nriPTW nt thp haeh chian tube leading to the pharynx; i,laby- 

whicii opens at tne oacx rinth>withsemicircularcanal8andcoch i e a 
part of the mouth. 3d. visible. 

The internal ear, or labyrinth, an irregular cavity in the 
solid part of the temporal bone, and separated from the 




180 


COMPARATIVE ZOOLOGY. 


middle ear by a bony partition, which is perforated by 
two small holes. The labyrinth consists of the vestibule , 
or entrance; the semicircular canals , or tubes; and the 
cochlea , or spiral canal. While the other parts are full of 
air, the labyrinth is filled with a liquid, and in this are 
the ends of the auditory nerve. The vibrations of the 
air, collected by the external ear, are concentrated upon 
the tympanum, and thence transmitted through the chain 
of little bones to the fluid in the labyrinth. 

Now, the essential organ of hearing is the labyrinth, 
which is, substantially, a bag filled with fluid and nerve- 
filaments. Fishes generally have but little more. In 
Amphibians and Reptiles there are added a tympanum, 
a single bone, connecting this with the internal ear, the 
cochlea, and the Eustachian tube; the tympanum being 
external. Birds have, besides, an auditory passage, open¬ 
ing on a level with the surface of the head, and surround¬ 
ed by a circle of feathers. Mammals only have an exter¬ 
nal ear . 93 

Sight is the perception of light . 93 In all animals it de¬ 
pends upon the peculiar sensitiveness of the optic organ to 
the luminous vibrations. In Vertebrates the optic nerve 
comes from the middle mass of the brain, in Invertebrates 
it is derived from a ganglion. Many animals are utter¬ 
ly destitute of visual organs, as the Protozoa, and the 
lower Radiates and Mollusks, besides intestinal Worms 
and the blind Fishes and other cave-animals. Around the 
margin of the Jelly-fish are colored spots, supposed to be 
rudimentary eyes; but, as a lens is wanting, there is no 
image; so that the creature can merely distinguish light 
from darkness and color without form. Such an eye is 
nothing but a collection of pigment granules on the ex¬ 
pansion of a nervous thread, and the perception of light 
is the sensation of warmth, the pigment absorbing the 
rays and converting them into heat. 


THE NERVOUS SYSTEM. 


181 




Going higher, we find a lens introduced forming a dis¬ 
tinct image. The Snail, for example, has two simple eyes, 
called ocelli, mounted on the tip of its long tentacles, con¬ 
sisting of a globular lens, 94 
with a transparent skin 
(cornea) in front, and a 
colored 
membrane 
(ch oroid) 
and a ner¬ 
vous n e t- 

Fig. i5B. — Eye of work (reti- 
Pecten, much en- v # 

larged: m,mouth; Iia) behind. 

I, lens; r, retina rrii o n 
and choroid ; n, 1 be Scallop 

nerve. ( Peden ) lias 

such eyes in the edge of 
its mantle (Fig. 153). Such 
organs are the only eyes 
possessed by Myriapods, 

Spiders, Scorpions, and 
Caterpillars. Adult In¬ 
sects usually have three ocelli on the top of the head. 
But the proper visual organs of Lobsters, Crabs, and In¬ 
sects are two compound eyes , perched 
on pedestals, or fixed on the sides of 
the head. They consist of an immense 
number of ocelli pressed together so 
that they take an angular form—four¬ 
sided in Crustacea, six-sided in Insects. 

They form two rounded protuberances 
variously colored—white, yellow, red, Fig. 155.—Head of the Bee, 

i i i tt i showingcompoundeyeg, 
green, purple, brown, or black. U nder the three ocelli, or stem- 

the microscope, the surface is seen to mata ’ and the antenn£e ' 

be divided into a host of facets, 95 each being an ocellus 

complete in itself. Each cornea is convex on one side, 


Fig. 154—Head of a Snail bisected, showing 
structure of tentacles: a, right inferior ten¬ 
tacle retracted within the body; 6, right su¬ 
perior tentacle fully protruded; c, left supe¬ 
rior tentacle partiaily inverted; d, left inferi¬ 
or tentacle; /, optic nerve; g, retractor mus¬ 
cle; h, optic nerve in loose folds; i, retractor 
muscle of head; k , nerve and muscle of left 
inferior tentacle; l, m, nervous collar. 















COMPARATIVE ZOOLOGY. 


182 


a 




and either convex or flat on the other, so that it produces 

a focus like a lens. Be¬ 


hind the cornea, or 
lens, is the pigment, 
having a minute aper¬ 
ture or “ pupil.” Next 
is a conical tube—one 


for each facet — with 


sides and bottom lined 


with pigment. These 
tubes converge to the 
optic ganglion, the 
fibres of which pass 
through the tubes to 
the cornea. 96 Vision 

J ig. 156.—Eye of ci Beetle (il 'IcloloTithct) i Aj section \ T \\7 miell POITHIOU11 (1 

a, optic ganglion; b, secondary nerves; c> retina ; •/ ^ 

d, pigment layer; e, proper optic nerves; B, group gye is not a mosaic ; 

of ocelli; /, bulb of optic nerve; g, layer of pig- ■ 

ment; h, vitreous humor ; i, cornea. blit each OCellllS gives 

a complete image, although a different perspective from 
its neighbor. The 
multiplied images are 
reduced to one men¬ 


tal stereoscopic pict¬ 
ure, on the principle 
of single vision in 
ourselves. 


The eyes of the 
Cuttle-fish are the 


largest and the most 
perfect among Inver¬ 
tebrates. They re¬ 
semble the eyes of 
higher animals in hav¬ 
ing a crystalline lens 
with a chamber in 


Fig. 157. —Section of Human Ej r e: a and 6, upper and 
lower lid; c, conjunctiva, or mucous membrane, 
lining the inner surface; d, external membrane; e, 
sheath of optic nerve; f, g, muscles for rolliug the 
eye up or down; h , sclerotic; i, transparent cor- 
nea;y, choroid; k, l, ciliary muscle for adjusting 
the eye for distance ; m, iris and pupil; n, canal; 
o, retina; s, vitreous humor; t, crystalline; r, an¬ 
terior chamber; x , posterior chamber. 

front (open, however, to the sea- 


















THE NERVOUS SYSTEM. 


183 


water), and a chamber behind it filled with “vitreous 
humor.” 

The eye of Vertebrates is formed by the infolding of 
the skin to create a lens, and an outgrowth of the brain 
to make a sensitive 
layer; both enclosed in 
a white spherical case 
(sclerotic ) made of 
tough tissue, with a 
transparent front, call¬ 
ed the cornea . This 
case is kept in shape 
by two fluids—the thin 
aqueous humor filling 
the cavity just behind 6 
the cornea, and the 
jelly-like vitreous hu¬ 
mor occupying the lar¬ 
ger posterior chamber. 

Between the two hu¬ 
mors lies the double- 
convex crystalline lens. 

On the front face of 
the lens is a contractile 
circular curtain (iris), 
with a hole in the cen¬ 
tre (pupil); and lin¬ 
ing the sclerotic coat 
is the choroid mem- 

U ranp pnvprprl with Fig. 158.—Section of the Human Retina, X 400: 1, 
uitiiie, vvitu interoal iimiting membrane; 2, op tic-nerve fibres; 

dark pigment. The 3, ganglion cells; 4, internal molecular layer; 5, 

r ® . interna] granules; 6, external molecular layer; 7, 

optic nerve, entering externalgranules; 8, external limitingmembrane; 

9, layer of rods and cones; 10, pigment layer. 

at the back of the eye J 

through the sclerotic and choroid coats, expands into the 
transparent retina, which consists of several layers — 


















































COMPARATIVE ZOOLOGY. 


184 

fibrous, cellular, and granular. The most sensitive part is 
the surface lying next to the black pigment. And here 
is a peculiarity of the vertebrate eye: the nerve-fibres, en¬ 
tering from behind, turn back and look towards the bot¬ 
tom of the eye, so that vision is directed backward; while 
invertebrate vision is directly forward. In Vertebrates 
only, the optic nerves cross each other ( decussate) in pass¬ 
ing from the brain to the eyes; so that the right side of 
the brain, e. g ., receives the impressions of objects on the 
left side of the body. 97 

Generally, the eyes of Vertebrates are on opposite sides 
of the head; but in the Flat-fishes both are on the same 
side. Usually, both eyes see the same object at once; but 
in most Fishes the eyes are set so far back, the fields of 
vision are distinct. The cornea may be flat, and the lens 
globular, as in Fishes; or the cornea very convex, and the 
lens flattened, as in Owls. Purely aquatic animals have 
neither eyelids nor tears, but nearly all others (especially 
Birds) have three lids. 98 The pupil is usually round; but 
it may be rhomb-shaped, as in Frogs; vertically oval, as 
in Crocodiles and Cats: or transversely oval, as in Geese, 
Doves, Horses, and Ruminants. Many Quadrupeds, as the 
Cat, have a membrane itapetum) lining the bottom of the 
eyeball, with a brilliant metallic lustre, usually green or 
pearly: it is this which makes the eyes of such animals 
luminous in the dark. 

2. Instinct and Intelligence. 

The simplest form of nervous excitement is mere sensa¬ 
tion. Above this we have sensation awakening conscious¬ 
ness, out of which come those voluntary activities grouped 
together under the name of Instinct; and, finally, Intelli¬ 
gence. 

The lowest forms of life are completely under law, for 
their movements seem to be due solely to their organiza- 



THE NERVOUS SYSTEM. 


185 


tion. They are automatons, or creatures of necessity. 
Such, also, are some actions in the higher animals, as 
breathing, the beating of the heart, the contractions of 
the iris, and all the first movements of an infant. 89 But, 
generally, the actions of animals are not the result of mere 
bodily organization. 

The inferior orders are under the control of Instinct, 
i. e ., an apparently untaught ability to perforin actions 
which are useful to the animal. 100 They seem to be born 
with a measure of knowledge and skill (as Man is said to 
have innate ideas), acquired neither by reason nor experi¬ 
ment. For what could have led Bees to imagine that by 
feeding a worker-larva with royal jelly, instead of bee- 
bread, it would turn out a queen, instead of a neuter? 
In this case, neither the habit nor the experience could be 
inherited, for the worker-bees are sterile. We can only 
guess that the discovery has been communicated by the 
survivors of an older swarm. Uniformity is another char¬ 
acteristic feature of instinct. Different individuals of the 
same species execute precisely the same movements under 
like circumstances. The career of one Bee is the career 
of any other. We do not find one clever and another 
stupid. Honey-combs are built now as they were before 
the Christian era. The creatures of pure instinct appear 
to be tied down, by the constitution of their nervous sys¬ 
tem, to one line of action, from which they cannot spon¬ 
taneously depart. The actions vary only as the structure 
changes. 101 There is a wonderful fitness in what they do, 
but there is no intentional adaptation of means to ends. 

All animals, from the Star-fish to Man, are guided more 
or less by instinct; but the best examples are furnished 
by the insect-world, especially by the social Hymenopters 
(Ants, Bees, and Wasps). The Butterfly carefully pro¬ 
vides for its young, which it is destined never to see; 
many Insects feed on particular species of plants, which 


186 


COMPARATIVE ZOOLOGY. 


they select with wonderful sagacity; and Monkeys avoid 
poisonous berries; Bees and Squirrels store up food for 
the future; Bees, Wasps, and Spiders construct with mar¬ 
vellous precision; and the subterranean chambers of Ants 
and the dikes of the Beaver show engineering skill; while 
Salmon go from the ocean up the rivers to spawn; and 
Birds of the temperate zones migrate with great regu¬ 
larity. 

But in the midst of this automatism there are the glim¬ 
merings of intelligence and free-will. We see some evi¬ 
dence of choice and of designed adaptation. Pure in¬ 
stinct should be infallible. Yet we notice mistakes that 
remind us of mental aberrations. Bees are not so eco¬ 
nomical as has been generally supposed. A mathemati¬ 
cian can make five cells with less wax than the Bee uses 
for four; while the Humble-bee uses three times as much 
material as the Hive bee. An exact hexagonal cell does 
not exist in nature. Flies lay eggs on the carrion-plant 
because it happens to have the odor of putrid meat. The 
domesticated Beaver will build a dam across its apartment. 
Birds frequently make mistakes in the construction and 
location of their nests. In fact, the process of cheating 
animals relies on the imperfection of instinct. Hor are 
the actions of the brute creation always perfectly uni¬ 
form ; and, so far as animals conform to circumstances, 
they act from intelligence, riot instinct. There is proof 
that some animals profit by experience. Birds do learn 
to make their nests; and the older ones build the best. 
Trappers know well that young animals are more easily 
caught than old ones. Birds brought up from the egg, 
in cages, do not make the characteristic nests of their 
species; nor do they have the same song peculiar to their 
species, if they have not heard it. Chimney-swallows cer¬ 
tainly built their nests differently in America three hun¬ 
dred years ago. A Bee can make cells of another shape, 


THE NERVOUS SYSTEM. 


187 


for it sometimes does; its actions, therefore, being elec¬ 
tive and conditional, are in a measure the result of calcu¬ 
lation. 

The mistakes and variations of instinct are indications 
that animals have something more — a limited range of 
that principle of Intelligence so luminous in Man. No 
precise line can be drawn between instinctive and intel¬ 
ligent acts; all we can say is, there is more freedom of 
choice in the latter than the former; and that some ani¬ 
mals are most instinctive, others most intelligent. Thus, 
we speak of the instinct of the Ant, Bee, and Beaver, 
and the intelligence of the Elephant, Dog, and Monkey. 
Instinct loses its peculiar character as intelligence becomes 
developed. Ascending from the Worm and Oyster to 
the Bee, we see the movements become more complex in 
character and more special in their objects; but instinct 
is supreme. Still ascending, we observe a gradual fading- 
away of the instincts, till they become subordinate to 
higher faculties—will and reason. We can predict with 
considerable certainty the actions of animals guided by 
pure instinct; but in proportion as they possess the power 
of adapting means to ends, the more variable their actions. 
Thus, the architecture of Birds is not so uniform as that 
of Insects. 108 

We must credit brutes with a certain amount of obser¬ 
vation and imitation, curiosity and cunning, memory and 
reason. Animals have been seen to pause, deliberate, or 
experiment, and resolve. The Elephant and Horse, Dog 
and Monkey, particularly, participate in the rational nat¬ 
ure of Man, up to a certain point. Thinking begins wher¬ 
ever there is an intentional adaptation of means to ends; 
for that involves the comparison and combination of ideas. 
Animals interchange ideas: the whine of a Dog at the 
door on a cold night certainly implies that he wants to 
be let in. Bees and Ants, it is well known, confer by 


188 


COMPARATIVE ZOOLOGY. 


passing their antennae. All the higher animals, too, have 
similar emotions—as joy, fear, love, and anger. 

While instinct culminates in Insects, the highest devel¬ 
opment of intelligence is presented in Man. 103 In Man 
only does instinct cease to be the controlling power. He 
stands alone in having the whole of his organization con¬ 
formed to the demands of his brain; and his intelligent 
acts are characterized by the capacity for unlimited prog¬ 
ress. The brutes can be improved by domestication; 
but, left to themselves, they soon relapse into their origi¬ 
nal wildness. Civilized Man also goes back to savagery; 
yet Man (though not all Men) has the ambition to exalt 
his mental and moral nature. He has a soul, or conscious 
relation to the Infinite, which leads him to aspire after a 
lofty ideal. Only he can form abstract ideas. And, 
finally, he is a completely self-determining agent, with a 
prominent will and conscience—the highest attribute of 
the animal creation. In all this, Man differs profoundly 
from the lower forms of life. 

3. The Voices of Animals. 

Most aquatic animals are mute. Some Crabs make 
noises by rubbing their fore-legs against their carapace; 
and many Fishes produce noises in various ways, mostly 
by means of the swim-bladder. Insects are the Inverte¬ 
brates which make the most noise. Their organs are usu¬ 
ally external, while those of Vertebrates are internal. In¬ 
sects of rapid flight generally make the most noise. In 
some the noise is produced by friction (stridulation); in oth- 
ers, by the passage of air through the spiracles (humming). 
The shrill notes of Crickets and Grasshoppers are pro¬ 
duced by rubbing the wings against each other, or against 
the thighs; but the Cicada, or Harvest-fly, has a special 
apparatus—a tense membrane on the abdomen, acted upon 
by muscles. The buzzing of Flies and humming of Bees 




THE NERVOUS SYSTEM. 


189 


are caused, in part, by the vibrations of the wings; but 
the true voice of these Insects comes from the spiracles 
of the thorax. 

Snakes and Lizards have no vocal cords, and can only 
hiss. Frogs croak 104 and Crocodiles roar, and the huge 
Tortoise of the Galapagos Islands utters a hoarse, bellow¬ 
ing noise. 

The vocal apparatus in Birds is situated at the lower 
end of the trachea, where it divides into the two brom 
chi. 105 It consists mainly of a bony drum, with a cross¬ 
bone, having a vertical membrane attached to its upper 
edge. The membrane is put in motion by currents of air 
passing on either side of it. Five pairs of muscles (in the 
Songsters) adjust the length of the windpipe to the pitch 
of the glottis. The various notes are produced by differ¬ 
ences in the blast of air, as well as by changes in the ten¬ 
sion of the membrane. The range of notes is commonly 
within an octave. Birds of the same family have a simi¬ 
lar voice. All the Parrots have a harsh utterance; Geese 
and Ducks quack; Crows, Magpies, and Jays caw; while 
the Warblers differ in the quality, rather than the kind, of 
note. 106 The Parrot and Mocking-bird use the tongue in 
imitating human sounds. Some species possess great com¬ 
pass of voice. The Bell-bird can be heard nearly three 
miles; and Livingstone said he could distinguish the voices 
of the Ostrich and the Lion only by knowing that the for¬ 
mer roars by day, and the latter by night. 

The vocal organ of Mammals, unlike that of Birds, is 
in the upper part of the larynx. It consists of four car¬ 
tilages, of which the largest (the thyroid) produces the 
prominence in the human throat known as “Adam’s ap¬ 
ple,” and two elastic bands, called “ vocal cords,” just be¬ 
low the glottis, or upper opening of the windpipe. The 
various tones are determined by the tension of these cords, 
which is effected by the raising or lowering of the thyroid 


190 


COMPARATIVE ZOOLOGY. 



cartilage, to which one end of the cords is attached. The 
will cannot influence the contraction of the vocalizing 
muscles, except in the very act of vocalization. The vo¬ 
cal sounds produced by Mammals may be 
distinguished into the ordinary voice, the 
cry, and the song. The second is the sound 
made by brutes. The Whale, Porpoise, Ar¬ 
madillo, Ant-eater, Porcupine, and Giraffe 
are generally silent. The Bat’s voice is 
probably the shrillest sound audible to hu- 
F,a 159.— Human man ears. There is little modulation in 

Larynx, seen in 

profile; a, half brute utterance. The Opossum purrs, the 

bone ; e, tra- Sloth and Kangaroo moan, the Hog grunts 

or s i ueals > the Ta P ir whistles > the Sta s bel - 

ti8, lows, and the Elephant gives a hoarse trump¬ 

et sound from its trunk and a deep groan from its throat. 
All Sheep have a guttural voice; all the Cows low, from 
the Bison to the Musk-ox; all the Horses and Donkeys 
neigh; all the Cats miau , from the domestic animal to the 
Lion; all the Bears growl; and all the Canine family— 
Fox, Wolf, and Dog — bark and howl. The Howling- 
monkeys and Gorillas have a large cavity, or sac, in the 
throat for resonance, enabling them to utter a powerful 
voice; and one of the Gibbon-apes has the remarkable 
power of emitting a complete octave of musical notes. 
The human voice, taking the male and female together, 
has a range of nearly four octaves. Man’s power of speech, 
or the utterance of articulate sounds, is due to his intel¬ 
lectual development rather than to any structural differ¬ 
ence between him and the Apes. Song is produced by 
the vocal cords, speech by the mouth. 


REPRODUCTION. 


191 


CHAPTER XIX. 


REPRODUCTION. 

It is a fundamental truth that every living organism 
has had its origin in some pre-existing organism. The 
doctrine of “spontaneous generation,” or the supposed 
origination of organized structures out of inorganic parti¬ 
cles, or out of dead organic matter, has not yet been sus¬ 
tained by facts. 

Reproduction is of two kinds — sexual and asexual. 
All animals, probably, have the first method, while a very 
great number of the 
lower forms of life have 
the latter also. 

Of asexual reproduc¬ 
tion there are two kinds 
— Self - division and 
Budding. 

Self-division, the 
simplest mode possible, 
is a natural breaking-up 
of the body into distinct 
surviving parts. This 
process is sometimes ex¬ 
traordinarily rapid, the 
increase of one animal¬ 
cule (Paramoecium) be- 

in£ computed at 268 Fio. m— Reproduction of Infusoria ( Vorticel 

& , r T Ice and others) by fission or self-division. 

millions m a month. It 

may be either transverse or longitudinal. Of the first 
6ort, Figs. 1,2, and 3 (Fig. 160) are examples; of the latter, 



192 


COMPARATIVE ZOOLOGY. 


Figs. 4, 6, 9-13. This form of reproduction is, naturally, 
confined to animals whose tissues and organs are simple, 
and so can easily bear division, or whose parts are so ar¬ 
ranged as to be easily separable without serious injury. 
The process is most common in Protozoa, Worms, and 
Polyps. 

Budding is separated by no sharp line from Self-divi¬ 
sion. While in the latter a part of the organs of the par¬ 
ent go to the offspring, in the former one or more cells 
of the original animal begin to develop and multiply so 
as to grow into a new animal like the parent. The proc¬ 
ess in animals is quite akin to the same operation in 
plants. The buds may remain permanently attached to 
the parent-stock, thus making a colony, as in Corals and 
Bryozoa ( continuous budding ), or they may be detached 
at some stage of growth {discontinuous budding ). This 
separation may occur when the bud is grown up, as in 
Hydra (Fig. 191), or as in Plant-lice, Daphnias (Fig. 255), 
and among other animals the buds may be internal, and 
detached when entirely undeveloped and externally re¬ 
sembling an egg. They differ, however, entirely from a 
true egg in developing directly, without fertilization. 

Sexual Reproduction requires cells of two kinds, usu¬ 
ally from different animals. These are the germ-cell or 
egg, and the sperm-cell. The embryo is developed from 
the union of the two cells. 107 

The egg consists essentially of three parts, the germmal 
vesicle , the yolk , and the vitelline membrane , which sur¬ 
rounds both the first. It is ordinarily globular in shape. 
Of the three parts, the primary one is the germinal vesi¬ 
cle—a particle of protoplasm. The yolk serves as food 
for this, and the membrane protects both. When a great 
mass of yolk is present, it is divisible into two parts—/w- 
mative and food yolk. The latter is of a more oily nature 
than the former, and is usually not segmented with the 


REPRODUCTION. 


193 



egg. The structure of the hen’s egg is more complicated. 
The outside shell consists of earthy matter (lime) depos¬ 
ited in a net-work of animal matter. 

It is minutely porous, to allow the 
passage of vapor and air to and fro. 

Lining the shell is a double mem¬ 
brane (membrana putaminis) resem¬ 
bling delicate tissue-paper. At the 
larger end, it separates to enclose a 
bubble of air for the use of the chick. 

Next comes the albumen, or “ white,” 
in spirally arranged layers, within 
which floats the yolk. The yolk is 
prevented from moving towards either end of the egg by 
two twisted cords of albumen, called chalazcB; yet is al¬ 
lowed to rise towards one side, the yolk being lighter than 
the albumen. The yolk is composed of oily granules 
(about of an inch in diameter), enclosed in a sac, called 
the vitelline membrane , and disposed in concentric layers, 
like a set of vases placed one within the other. That part 
of the yolk which extends from the centre to a white 


Fio. 161. — Theoretical Egg, 
or Cell: r, vitelline mem¬ 
brane ; y, oleaginous pole; 
a, albuminous pole; p , 
Purkiujean, or germinal, 
vesicle; w, Wagnerian, or 
germinal, dot. 



Fig. 162. — Longitudinal Section of Hen’s Egg before incubation: a, yolk, showing 
concentric layers; a', its semi-fluid centre, consisting of a white granular sub¬ 
stance—the whole yolk is enclosed in the vitelline membrane; b, inner dense 
part of the albumen ; outer, thinner part; c, the chalazse, or albumen, twisted 
by the revolutions of the yolk; d, double shell-membrane, split at the large end 
to form the chamber,/; e t the shell; h , the white spot, or cicatricula. 

13 







194 


COMPARATIVE ZOOLOGY. 


spot ( cicatricula') on the outside cannot be hardened, even 
with the most prolonged boiling. The cicatricula, or em¬ 
bryo-spot—the part for which all the rest was made—is 
a thin disk of cellular structure, in which the new life 
first appears. This was originally a simple cell, but de¬ 
velopment has gone some way before the egg is laid. It 
is always on that side which naturally turns uppermost, 
for the yolk can turn upon its axis; it is, therefore, al¬ 
ways nearest to the external air and to the Hen’s body— 
two conditions necessary for its development. There is 
another reason for this polarity of the egg: the lighter 
and most delicate part of the yolk is collected in its 
upper part, while the heavy, oily portion remains be¬ 
neath. 

In most eggs the shell and albumen are wanting. When 
the albumen is present, it is commonly, covered by a mem¬ 
brane only. In Sharks, the envelope is horny; and in 
Crocodiles it is calcareous, as in Birds. 

The egg of the Sponge has no true vitelline membrane, 
and is not unlike an ordinary amoeboid cell. An egg is, 
in fact, little more than a very large 
cell, of which the germinal vesicle is 
the nucleus. 

The size of an egg depends mainly 
upon the quantity of yolk it contains; 
and to this is proportioned the grade of 
development which the embryo attains 
when it leaves the egg . 108 In the eggs 
Fig. lea.—Egg of sponge, of the Star-fishes, Worms, Insects, Mol- 
lusks (except the Cuttle-fishes), many 
Amphibians, and Mammals, the yolk is very minute and 
formative, i. e. y it is converted into the parts of the future 
embryo. In the eggs of Lobsters, Crabs, Spiders, Cepha¬ 
lopoda Fishes, Keptiles, and Birds, the yolk is large and 
colored, and consists of two parts — the formative, or 



REPRODUCTION. 


195 


germ-yolk, immediately surrounding the germinal vesicle; 
and the nutritive, or food-yolk, constituting the greater 
part of the mass, by which the young animal in the egg- 
life is nourished. In the latter case, the young come forth 
more mature than where the food-yolk is wanting. 

As to form, eggs are oval or elliptical, as in Birds and 
Crocodiles; spherical, as in Turtles and Wasps; cylindri¬ 
cal, as in Bees and Flies; or shaped like a hand-barrow, 
with tendrils on the corners, as in the Shark. The eggs 



Fio. 164.—Egg of a Shark (the external gills of the embryo are not represented). 

of some very low forms are sculptured or covered with 
hairs or prickles. 

The number of eggs varies greatly in different animals, 
as it is in proportion to the risks during development. 
Thus, the eggs of aquatic tribes, being unprotected by the 
parent, and being largely consumed by many animals, are 
multiplied to prevent extinction. The spawn of a single 
Cod contains millions of eggs; that of the Oyster, 6,000,- 
000. A Queen-bee, during the five years of her existence, 
lays about a million eggs. 

Eggs are laid one by one, as by Birds; or in clusters, as 
by Frogs, Fishes, and most Invertebrates. The spawn of 
the Sea-snails consists of vast numbers of eggs adhering 
together in masses, or in sacs, forming long strings. 

As a rule, the higher the rank, the more care animals 


196 


COMPARATIVE ZOOLOGY. 


take of their eggs and their young, and the higher the 
temperature needed for egg-development. In the major- 
it } 7 of cases, eggs are left to themselves. The fresh-water 
Mussel (Unio) carries them within its gills, and the Lob¬ 
ster under its tail. The eggs of many Spiders are envel¬ 
oped in a silken cocoon, which the mother guards with 
jealous care. Insects, as Flies and Moths, deposit their 
eggs where the larva, as soon as born, can procure its own 
food. Most Fishes allow their spawn, or roe, to float in 
the water; but a few build a kind of flat nest in the sand 
or mud, hovering over the eggs until they are hatched; 
while the Acara of the Amazons carries them in its 
mouth. The Amphibians, generally, envelop their eggs 
in a gelatinous mass, which they leave to the elements; 
but the female of the Surinam Toad carries hers on her 
back, where they are placed by the male. The great Am¬ 
azon Turtles lay their eggs in holes two feet deep, in the 
sand; while the Alligators simply cover theirs with a few 
leaves and sticks. Nearly all Birds build nests, those of 
the Perchers being most elaborate, as their chicks are de¬ 
pendent for a time on the parent . 109 The young of Mar¬ 
supials, as the Kangaroo, 'which are born in an extremely 
immature state, are nourished in a pouch outside of the 
body. But the embryo of all other Mammals is devel¬ 
oped within the parent to a more perfect condition, by 
means of a special organ, the placenta. It is a general 
law, that animals receiving in the embryo state the longest 
and most constant parental care ultimately attain the high¬ 
est grade of development. 

The Protozoa, which have no true eggs, have a sort of 
reproduction called conjugation. In this process two 
Amoebae unite into one mass, surround themselves with a 
case, in which they divide into several parts, each portion 
becoming a new Amoeba. 

The sperm-cells differ from the egg in being very small, 


DEVELOPMENT. 


197 


usually motile, and in that a large number are usually 
produced from a single cell of the animal, while the egg 
represents an entire cell. The union of the sperm-cell 
with the germinal vesicle (fertilization) is the first step 
in development, and without it the egg will not develop. 
But the nature of the process is unknown. 


CHAPTER XX. 

DEVELOPMENT. 

Development is the evolution of a germ into a com¬ 
plete organism. The study of the changes within the egg 
constitutes the science of Embryology; the transforma¬ 
tions after the egg-life are called metamorphoses, and in¬ 
clude growth and repair. 

The process of development is a passage from the gen¬ 
eral to the special, from the simple to the complex, from 
the homogeneous to the heterogeneous, by a series of dif¬ 
ferentiations. It brings out first the profounder distinc¬ 
tions, and afterwards those more external. That is, the 
most essential parts appear first. And not only does de¬ 
velopment tend to make the several organs of an individ¬ 
ual more distinct from one another, but also the individual 
itself more distinguished from other individuals and from 
the medium in which it lives. With advancing develop¬ 
ment, the animal, as a rule, acquires a more specific, defi¬ 
nite form, and increases in weight and locomotive power. 
Life is a tendency to individuality. 

The first step in development, after fertilization, is the 
segmentation of the egg, by a process of self-division. In 
the simplest form, the whole yolk divides into two parts; 
these again divide, making four, eight, sixteen, etc., parts, 



198 


COMPARATIVE ZOOLOGY. 


until the whole yolk is subdivided into very small por¬ 
tions (cells) surrounding a central cavity. This stage is 
known as the “ mulberry-mass,” or blastula (Fig. 165, c). 

ABC 



Fig. 165.— First Stages in Segmentation of a Mammalian Egg: A, first division into 
halves, with spermatozoa around it; B aud C , progressive subdivision, ultimate¬ 
ly transforming the vitellus, or yolk, iuto a “mulberry mass” of globules, or em¬ 
bryo-cells. 


If the yolk is larger, relatively to the germinal vesicle, 
the process of division may go on more slowly in one of 
the two parts of the egg, first formed; or in very large 
eggs, like those of Birds and Cuttle-fishes, only a small 
part of the yolk subdivides. 

In some form, the process of segmentation is found in 
the eggs of all animals, as is also the following stage. 

This step is the differentiation of the 
single layer of cells into two parts, 
one for the body-wall, the other for 
the wall of the digestive tract. In 
the typical examples, this is accom- 
_____ plished by one part of the wall of 

Fig. 166.—Diagram of Gastru- the blastula turning in, so far as to 

la of a Worm (Sagitta): a, , ,, , , , ,. 

primitive mouth; b, primi- convert tlie blastula into a sort of 

pHmifivf b fc ody-ca a vUy y ; ; en t double-walled cup, the gastrula (Fig. 

endoderm; ec, ectoderm. 166). One half of tile Wall of the 

blastula is now the outer wall of the germ, the other half 
that of the digestive cavity; the original blastula-cavity 
is now the body-cavity, and the new cavity formed by the 
infolding is the stomach, and its opening is both mouth 






DEVELOPMENT. 


199 


and vent (Figs. 165, 166). Some adult animals are little 
more than such a sac. Hydra (Fig. 191), for instance, is 
little different from a gastrula with tentacles, and one of 
its relatives wants even these additions. 

Ordinarily, however, development goes much further. 
From the two original layers arises, in various ways, a third 
between them, making the three primitive germ-layers— 
epiblast , mesoblast , and hypoblast. This new layer is nec¬ 
essarily in the primitive body-cavity, which it may fill 
up; or usually a new body-cavity is formed, in different 
ways in different groups. In by far the great majority 
of animals the digestive tract gets a new opening, which 
usually becomes the mouth ; and the old mouth may 
close, or serve only the functions of the vent. From this 
point the development of each group must be traced in 
detail. 

Development of a Hen’s Egg. — After the segmentation 
the germinal disk divides into two layers, between which 
a third is soon formed. The upper layer ( epiblast ) gives 



Fig. 167.—Vertical Sections of an Egg, showing progressive stages of-development: 
a, notochord; b, medullary furrow, becoming a closed canal in the last. 

rise to the cuticle, brain, spinal cord, retina, crystalline 
lens, and internal ear. From the lower layer (hypoblast) 
is formed the epithelium of the digestive canal. From 
the middle layer (mesoblast) come all the other organs— 
muscles, nerves, bones, etc. The mesoblast thickens so 
as to form two parallel ridges running lengthwise of 
the germ, and leaving a groove between them (medul¬ 
lary furrow and ridges). 110 The ridges gradually rise, 
carrying with them the epiblast, incline towards each oth¬ 
er. and at last unite along the back. So that we have a 



200 


COMPARATIVE ZOOLOGY. 


tube of epiblast surrounded by mesoblast, which is itself 
covered by epiblast. This tube becomes the brain and 
spinal cord, whose central canal, enlarging into the ven¬ 


tricles of the brain, tells the story of its original forma¬ 


tion. Beneath the furrow, a delicate cartilaginous thread 
appears (called notochord )—the predecessor of the back¬ 
bone. Meanwhile the mesoblast has divided into two 
layers, except in the middle of the animal, beneath the 
spinal cord, and in the head. One of these layers remains 
attached to the epiblast, and with it forms the body-wall; 
the other bends rapidly downward, carrying the hypoblast 
with it, and forms the wall of the intestine. The space 
thus left between the layers of the mesoblast is the body- 
cavity. At the same time, the margin of the germ ex¬ 
tends farther and farther over the yolk, till it completely 
encloses it. So that now we see two cavities — a small 
one, containing the nervous system; and a larger one be¬ 
low, for the digestive organs. Presently, numerous rows 


of corpuscles are seen 
on the middle layer, 
which are Subsequent¬ 



ly enclosed, forming a 



iu. ioo.— xiuuimeuiary neuris, Human: i, venous * 

trunks; 2, auricle; 3, ventricle ; 4, bulbus arte- called the vascular area. 

riosus. , . , . ... 

A dark spot indicates 


the situation of the heart, which is the first distinctly 
bounded cavity of the circulatory system. It is a short 
tube lying lengthwise just behind the head, with a feeble 
pulsation, causing the blood to flow backward and for¬ 
ward. The tube is gradually bent together, until it forms 
a double cavity, resembling the heart of a Fish. On the 
fourth day of incubation, partitions begin to grow, divid¬ 
ing the cavities into the right and left auricles and ven¬ 
tricles. The septum between the auricles is the last to 
be finished, being closed the moment respiration begins. 


DEVELOPMENT. 



201 

The blood-vessels ramify in all directions through the 
yolk, making it a spongy mass, and all perform the same 
office; it is not till the fourth or fifth day that arteries 
can be distinguished from veins, by being thicker, and by 
carrying blood only from the heart . 111 


Fig. 169.—Embryo in a Hen’s Egg during the first five days: A, hypoblast; B, lower 
layer of mesoblast; C, upper layer of mesoblast and epiblast united, in the last 
figures forming the amniotic sac; D, vitelline membrane; e, thickened blasto¬ 
derm, the first rudiment of the dorsal part (in the last figure it marks the place 
of the lungs); h, heart; a, b, its two chambers; c, aortic arches; m, aorta; i, 
liver; p, allantois. 












COMPARATIVE ZOOLOGY. 


202 

The embryo lies with its face, or ventral surface, tow¬ 
ards the yolk, the head and tail curving towards each 



Fio. 1 TO. —Hen’s Eg", more highly developed. The embryo is enveloped by the am¬ 
nion, and has the umbilical vessel, or remnant of the yolk, hanging from its un¬ 
der surface; while the allantois turns upward, and spreads ont over the internal 
surface of the shell-membrane. (Prom Dalton’s “ Physiology.”) 



other. Around the embryo on all sides the epiblast and 
upper layer of the mesohlast rise like a hood over the 

back of the embryo till they 


form a closed sac, called the 
amnion. It is filled with a 
thin liquid, which serves to 
protect the embryo. Mean¬ 
while, another important or¬ 
gan is forming on the other 
side. From the hinder por¬ 
tion of the alimentary canal 
an outgrowth is formed 

Fu,!!, Mammalian Embryo with al- which extends bey Olid the 
iantois tally formed: 1, umbilical vesi- J 

cle, containing the last of the yolk; 2, wall of tile embryo proper 
amnion; 3, allantois, on which thefringes . . O' r r . 

of the placenta are developing. (Prom into the Cavity of the amni- 
Dalton’s “ Physiology.’’) 

on and spreads out over the 
whole inner surface of the shell, so that it partly surrounds 
both embryo and inner layer of the amnion (amnion jprop- 




DEVELOPMENT. 


203 


er). This is the allantois. It is full of blood-vessels, and 
it serves as the respiratory organ until the chick picks the 
shell and breathes by its lungs. 112 The chorion is the out¬ 
ermost part of the allantois, and th q placenta of Mammals 
is the shaggy, vascular edge of the chorion. 

The alimentary canal is at first a straight tube closed at 
both ends, the middle being connected with the yolk-bag. 
As it grows faster than the body, it is thrown into a spi¬ 
ral coil; and at several points it dilates, to form the crop, 
stomach, gizzard, etc. The mouth is developed from an 
infolding of the skin. The liver is an outgrowth from 
the digestive tube, at first a cluster of cells, then of folli¬ 
cles, and finally a true gland. The lungs are developed 
on the third day as a minute bud from the upper part of 
the alimentary canal, or pharynx. As they grow in size, 
they pass from a smooth to a cellular condition. 

The skeleton at the beginning consists, like the noto¬ 
chord, of a cellular material, which gradually turns to car¬ 
tilage. Then minute canals containing blood-vessels arise, 
and earthy matter (chiefly phosphate of lime) is deposited 
between the cells. The primary bone thus formed is 
compact: true osseous tissue, with canaliculi, laminae, and 
Haversian canals, is the result of subsequent absorption. 113 
Certain bones, as those of the face and cranium, are not 
preceded by cartilage, but by connective tissue: these are 
called membrane bones. Ossification, or bone-making, be¬ 
gins at numerous distinct points, called centres; and, the¬ 
oretically, every centre stands for a bone, so that there are 
as many bones in a skeleton as centres of ossification. 
But the actual number in the adult animal is much small¬ 
er, as many of the centres coalesce. 114 The development 
of the backbone is not from the head or from the tail, but 
from a central point midway between : there the first ver¬ 
tebrae appear, and from thence they multiply forward and 
backward. 


204 


COMPARATIVE ZOOLOGY. 


The limbs appear as buds on the sides of the body; 
these lengthen and expand so as to resemble paddles— 
the wings and legs looking precisely alike; and, finally, 
they are divided each into three segments, the last one 
subdividing into digits. The feathers are developed from 
the outside cells of the epidermis: first, a horny cone is 
formed, which elongates and spreads out into a vane, and 
this splits up into barbs and barbules. 

The muscle-fibres are formed either by the growth in 
length of a single cell, or by the coalescence of a row of 
cells: the cell-wall thus produces a long tube—the sarco- 
lemma of a fibre—and the granular contents arrange them¬ 
selves into linear series, to make fi bridge. 

Nervous tissue is derived from the multiplication and 
union of embryo-cells. The white fibres at first resemble 
the gray. The brain and spinal marrow are developed 
from the epiblastic lining of the medullary furrow. Soon 
the brain, by two constrictions, divides into fore-brain, 
mid-brain, and hind-brain. The fore-brain throws out 
two lateral hemispheres (cerebrum), and from these pro¬ 
trude forward the two olfactory lobes. From the mid¬ 
dle-brain grow the optic lobes; and the hind-brain is 
separated into cerebellum and medulla oblongata. The 
essential parts of the eye, retina and crystalline lens, are 
developed, the former as a cup-like outgrowth from the 
fore-brain, the latter as an ingrowth of the epidermis. 
An infolding of the epidermis gives rise to the essential 
parts of the inner ear, and from the same layer come the 
olfactory rods of the nose and the taste-buds of the tongue. 
So that the central nervous system and the essential parts 
of most of the sense-organs have a common origin. 

Modes of Development.— The structure and embryology 
of a Hen’s egg exhibit many facts which are common 
to all animals. But every grand division of the Animal 
Kingdom has its characteristic method of developing. 


DEVELOPMENT. 


205 


Protozoans differ from all higher forms in having no 
true eggs. 

The egg of the Hydroid, after segmentation, becomes a 
hollow, pear-shaped body, covered with cilia. Soon one 
end is indented; then the indentation deepens until it 
reaches the interior and forms the mouth. The animal 
fastens itself by the other end, and the tentacles appear 
as buds. In the Sea-anemone, the stomach is turned in, 
and the partitions appear in pairs. 

In the Oyster, the egg segments into two unequal parts, 
one of which gives rise to the digestive tract and its de¬ 
rivatives, while from the smaller part originate the skin, 
gills, and shell. It is soon covered with cilia, by whose 
help it swims about. 

The embryo of an Insect shows from the first a right 
and left side; but the first indication that it is an Articu¬ 
late is the development of a series of indentations divid¬ 
ing the body into successive rings, or joints. Next, we 
observe that the back lies near the centre of the egg, the 
ventral side looking outward; i. e ., the embryo is doubled 
upon itself backward. And, finally, the appearance of 
three pairs of legs proves that it will be an Insect, rather 
than a Worm, Crustacean, or Spider. 

The Vertebrate embryo lies with its stomach towards 
the yolk, reversing the position of the Articulate; but the 
grand characteristic is the medullary groove, which does 
not exist in the egg of any Invertebrate. This feature is 
connected with another, the setting apart of two distinct 
regions — the nervous and nutritive. There are three 
modifications of Vertebrate development: that of Fishes 
and Amphibians, that of True Reptiles and Birds, and 
that of Mammals. The amnion and allantois are wanting 
in the first group; while the placenta (which is the allan¬ 
tois vitally connected with the parent) is peculiar to Mam¬ 
mals. In Mammals, the whole yolk is segmented; in 


206 


COMPARATIVE ZOOLOGY. 


Birds, segmentation is confined to the small white speck 
seen in opening the shell. 

At the outset, all animals, from the Sponge to Man, 
appear essentially alike. All, moreover, undergo seg¬ 
mentation, and most have one form or other of the 
gastrula stage. But while Vertebrates and Invertebrates 
can travel together on the same road up to this point, 
here they diverge—never to meet again. For every grand 
group early shows that it has a peculiar type of construc¬ 
tion. Every egg is from the first impressed with the 
power of developing in one direction only, and never does 
it lose its fundamental characters. The germ of the Bee 
is divided into segments, showing that it belongs to the 
Articulates; the gertn of the Lion has the medullary 
stripe—the mark of the coming Vertebrate. The blasto¬ 
dermic layer of the Vertebrate egg rolls up into two tubes 
—one to hold the viscera, the other to contain the nervous 
cord; while that of the Invertebrate egg forms only one 
such tubular division. The features which determine the 
subkingdom to which an animal belongs are first devel¬ 
oped, then the characters revealing its class. 

There are differences also in grade of development as 
well as type. For a time there is no essential difference 
between a Fish and a Mammal: they have the same ner¬ 
vous, circulatory, and digestive systems. There are many 
such cases, in which the embryo of an animal represents 
the permanent adult condition of some lower form. In 
other words, the higher species, in the course of their de¬ 
velopment, offer likenesses, or analogies, to finished lower 
species. The human germ, at first, cannot be distinguished 
from that of any other animal: for aught we can see, it 
may turn out a Frog or a Philosopher. The appearance 
of a medullary stripe excludes it at once from all Inverte¬ 
brates. It afterwards has, for a time, structures found in 
the lower classes and orders of Vertebrates as permanent 


DEVELOPMENT. 


207 


organs. For a time, indeed, the human embryo so closely 
resembles that of the lower forms as to be indistinguisha¬ 
ble from them; but certain structures belonging to those, 
forms are kept long after the embryo is clearly human. 115 
All the members of a group do not reach the same degree 
of perfection, some remaining in what corresponds to the 
immature stages of the higher animals. Such may be 
called permanently embryonic forms. 

Sometimes an embryo develops an organ in a rudimen¬ 
tary condition, which is lost or useless in the adult. Thus, 
the Greenland Whale, when grown up, has not a tooth in 
its head, while in the embryo life it has teeth in both 
jaws; unborn Calves have canines and upper incisors; 
and the female Dugong has tusks which never cut the 
gum. The “splint-bones” in the Horse’s foot are unfin¬ 
ished metatarsals. 

Animals differ widely in the degree of development 
reached at ovulation and at birth. The eggs of Frogs 
are laid when they can hardly be said to have become 
fully formed as eggs. The eggs of Birds are laid when 
segmentation is complete, while the eggs of Mammals are 
retained by the parent till after the egg-stage is passed. 116 
Ruminants and terrestrial Birds are born with the power 
of sight and locomotion. Most Carnivores, Rodents, and 
perching Birds come into the world blind and helpless; 
while the human infant is dependent for a much longer 
time. 

1. Metamorphosis. 

Few animals come forth from the egg in perfect condi¬ 
tion. The vast majority pass through a great variety of 
forms before reaching maturity. These metamorphoses 
(which are merely periods of growth) are not peculiar to 
Insects, though more apparent in them. Man himself is 
developed on the same general principles as the Butterfly,, 
but the transformations are concealed from view. The 


208 


COMPARATIVE ZOOLOGY. 


Coral, when hatched, has six pairs of partitions; after¬ 
wards, the spaces are divided by six more pairs; then 
twelve intermediate pairs are introduced; next, twenty- 
four, and so on. The embryonic Star-fish has a long 
body, with six arms on a side, in one end of which the 
young Star-fish is developed. Soon the twelve-armed 
body is absorbed, and the young animal is of age. 
Worms are continually growing by the addition of new 
segments. Nearly all Insects undergo complete metamor¬ 
phosis, i. e., exhibit four distinct stages of existence—egg, 
larva, pupa, and imago. The worm-like larva 117 may be 
called a locomotive-egg. It has little resemblance to the 
parent in structure or habits, eating and growing rapidly. 
Then it enters the pupa state, wrapping itself in a cocoon, 
or case, and remaining apparently dead till new organs 
are developed; when it escapes a perfect winged Insect, 



Fig. 172.—Butterfly in the Imago, Pupa, and Larva States. 


or imago. 118 Wings never exist externally in the larva; 
and some Insects which undergo no apparent metamor¬ 
phosis, as Lice, are wingless. The Grasshopper develops 
from the young larva to the winged adult without chang- 


DEVELOPMENT. 


209 


ing its mode of life. In the development of the common 
Crab, so different is the outward form of the newly 



Fig. 173.—Metamorphosis of the Mosquito (Culexpipiem ): A, boat of eggs; B, some 
of the eggs highly magnified; d, with lid open for the escape of the larva, C; D, 
pupa; E, larva magnified, showing respiratory tube, e, anal fins,/, antennae, g; 
F, imago; a, antennae; b, beak. 

hatched embryo from that of the adult, that the former 
has been described as a distinct species. 

The most remarkable example of metamorphosis among 
Vertebrates is furnished by the Amphibians. A Tadpole 
—the larva of the Frog—has a tail, but no legs; gills, in¬ 
stead of lungs; a heart precisely like that of the Fish; a 
horny beak for eating vegetable food, and a spiral intes¬ 
tine to digest it. As it matures, the hinder legs show 
themselves, then the front pair; the beak falls off; the 
tail and gills waste away; lungs are created; the diges¬ 
tive apparatus is changed to suit an animal diet; the heart 
is altered to the Reptilian type by the addition of another 
auricle; in ffact, skin, muscles, nerves, bones, and blood¬ 
vessels vanish, being absorbed atom by atom, and a'new 
set is substituted. Moulting , or the periodical renewal of 
epidermal parts, as the shell of the Lobster, the skin of 

14 






COMPARATIVE ZOOLOGY. 


210 

the Toad, the scales of Snakes, the feathers of Birds, and 
the hair of Mammals, may, be termed a metamorphosis. 



Fig. 174.—Metamorphosis of the Newt. 


The change from milk-teeth to a permanent set is another 
example. 

An animal rises in organization as development ad¬ 
vances. Thus, a Caterpillar’s life has nothing nobler 
about it than the ability to eat, while the Butterfly ex¬ 
pends the power garnered up by the larva in a gay and 
busy life. But there are seeming reversals of this law. 
Some mature animals appear lower in the scale than their 
young. The larval Cirripede has a pair of magnificent 
compound eyes and complex antennae; when adult, the 
antennae are gone, and the eyes are reduced to a single, 
simple, minute eye-spot. So the germs of the sedentary 
Sponge and Oyster are free and active. The adult ani¬ 
mal, however, is always superior in alone possessing the 
power of reproduction. Such a process is known as retro¬ 
grade metamorphosis. 

There are certain larval forms so characteristic of the 





DEVELOPMENT. 


211 




great groups of the animal kingdom as to demand notice. 
Most Worms leave the egg as a larva, called the trocho- 
sphere (Fig. 175), an oval larva, having mouth 
and anus, and a circle of cilia anterior to the 
mouth. This larval stage is common to Worms 
with the most diverse adult forms and habits. 

It is also found in all the great groups of Mol- ^oJph^of 
lusks. Clams, Snails, and Cuttle-fish all have worm(Phyi- 

. iodoce): a, 

the stage represented in their history. 1 he Mol- circle of cilia, 
lusks usually pass through a later stage called the veliger 

(Fig. 176), in which 
a circle of cilia ho¬ 
mologous to that of 
the trochosphere is 
borne by a lobed 
expansion on the 
head, called the ve¬ 
lum , or sail. The 
Crustacea, which 
exhibit so great a 
range of form in the adult state, all pass through a stage 
in which they are substantially alike. Forms as different 
in appearance as Barnacles, Entomostracans, and Prawns 
hatch out as Nauplii , little oval animals, with a straight 
intestine, three pairs of legs, and a simple eye (Fig. 177). 
See Figs. 253, 254, 255, 256. Fig. 256 represents the 
Lobster, which does not hatch as a Nauplius, but is not 
very unlike the Prawn. These larval forms are of great 
interest, because they disclose the relationships of the 
adult forms, as the gastrula stage hints at the common 
relationships of all animals above Protozoa. 

2. Alternate Generation . 

Sometimes a metamorphosis extending over several 
generations is required to evolve the perfect animal; “ in 


Fig. 176 _Larval Gasteropoda: A, B, Trochus; C, Ter- 

gipes ; a,, trochosphere ; v, velum ; B, veliger ; d, 
mouth; /, foot; s, shell; C, veliger; d, foot; c, tenta¬ 
cle ; b, ear. 


212 


COMPARATIVE ZOOLOGY. 



Fig. 177_Nauplius of Entomostracan ( Canthocamptus ). See Fig. 255. A, first an¬ 

tenna ; An, second antenna; a, anus; L, labrum; 0, ocellus; S, stomach. (From 
Brooks, after Hoek.) 

other words, the parent may find no resemblance to him¬ 
self in any of his progeny, until he comes down to the 
great-grandson.” Thus, the Jelly-fish, or Medusa, lays 
eggs which are hatched into larvae resembling Infusoria— 
little transparent oval bodies covered with cilia, by which 
they swim about for a time till they find a resting-place. 
One of them, for example, becoming fixed, develops rap¬ 
idly ; it elongates and spreads at the upper end; a mouth 
is formed, opening into a digestive cavity; and tentacles 
multiply till the mouth is surrounded by them. At this 
stage it resembles a Hydra. Then slight wrinkles appear 
along the body, which grow deeper and deeper, till the 
animal looks like “a pine-cone surmounted by a tuft of 
tentaclesand then like a pile of saucers (about a dozen 


DEVELOPMENT. 


213 


.in number) with scalloped edges. Next, the pile breaks 
up into separate segments, which are, in fact, so many dis¬ 
tinct animals; and each turning over as it is set free, so 
as to bring the mouth below, develops into an adult Me¬ 
dusa, becoming more and more convex, and furnished 
with tentacles, circular canals, and other organs exactly 
like those of the progenitor that laid the original egg. 

Here we see a Medusa producing eggs which develop 
into stationary forms resembling Hydras. The Hydras 



F ig . 178_Alternate Generation: a, b, c, ova of an Acaleph (Chrysaora) ; d,e,/, Hy¬ 

dras ; g } h, Hydras with constrictions; i, Hydra undergoing fission; k, one of the 
separated segments, a free Medusa. 

then produce not only Medusae by budding in the manner 
described, but also other Hydras like themselves by bud¬ 
ding. All these intermediate forms are transient states 
of the Jelly-fish, but the metamorphoses cannot be said to 
occur in the same individual. While a Caterpillar becomes 
a Butterfly, this Hydra-like individual produces a number 
of Medusae. Alternate generation is, then, an alternation 
of asexual and sexual methods of reproduction, one or 
more generations produced from buds being followed by 
a single generation produced from eggs. Often, as in 
the fresh-water Hydra, the two kinds of generations are 
alike in appearance. The process is as wide-spread as 
asexual reproduction, being found mostly in Sponges, 
Ccelenterates, and Worms. It is also found in certain 



214 


COMPARATIVE ZOOLOGY. 


Crustacea and Insects. The name is sometimes limited to 
cases where the two kinds of generations differ in form. 

3. Growth and Repair. 

Growth is increase of bulk, as Development is increase 
of structure. It occurs whenever the process of repair 
exceeds that of waste, or when new material is added 
faster than the tissues are destroyed. There is a specific 
limit of growth for all animals, although many of the low 
cold-blooded forms, as the Trout and Anaconda, seem to 
grow as long as they live. After the body has attained 
its maturity, i. e., has fully developed, the tissues cease to 
grow; and nutrition is concerned solely in supplying the 
constant waste, in order to preserve the size and shape of 
the organs. A child eats to grow and repair; the adult 
eats only to repair. 11 * Birds develop rapidly, and so spend 
most of their life full-fledged; while Insects generally, 
Fishes, Amphibians, Reptiles, and Mammals mature at 
a comparatively greater age. The perfect Insect rarely 
changes its size, and takes but little food; eating and 
growing are almost confined to larval life. The crust of 
the Sea-urchin, which is never shed, grows by the addition 
of matter to the margins of the plates. The shell of the 
Oyster is enlarged by the deposition of new laminae, each 
extending beyond the other. At every enlargement, the 
interior is lined with a new nacreous layer; so that the 
number of such layers in the oldest part of the shell indi¬ 
cates the number of enlargements. When the shell has 
reached its full size, new layers are added to the inner 
surface only, which increases the thickness. It is the 
margin of the mantle which provides for the increase in 
length and breadth, while the thickness is derived from 
the whole surface. The edges of the concentric laminae 
are the “ lines of growth.” The Oyster is full-grown in 
about five years. The bones of Fishes and Reptiles are 


DEVELOPMENT. 


215 


continually growing; the long bones of higher animals 
increase in length so long as the ends (epiphyses) are sep¬ 
arate from the shaft. The limbs of Man, after birth, 
grow more rapidly than the trunk. 

The power of regenerating lost parts is greatest where 
the organization is lowest, and while the animal is in the 
young or larval state. It is really a process of budding. 
The upper part of the Hydra, if separated, will reproduce 
the rest of the body; if the lower part is cut off, it will 
add the rest. Certain Worms may be cut into several 
pieces, and each part will regain what is needed to com¬ 
plete the mangled organism. The Star-fish can reproduce 
its arms; the Holothurian, its stomach ; the Snail, its ten¬ 
tacles; the Lobster, its claws; the Spider, its legs; the 
Fish, its fins; and the Lizard, its tail. Nature makes no 
mistake by putting on a leg where a tail belongs, or join¬ 
ing an immature limb to an adult animal. 120 In Birds and 
Mammals, the power is limited to the reproduction of cer¬ 
tain tissues, as shown in the healing of wounds. Very 
rarely an entire human bone, removed by disease or sur¬ 
gery, has been restored. The nails and hair continue to 
grow in extreme old age. 

4. Likeness and Variation. 

It is a great law of reproduction that all animals tend 
to resemble their parents. A member of one class never 
produces a member of another class. The likeness is very 
accurate as to general structure and form. But it does 
not descend to every individual feature and trait. In 
other words, the tendency to repetition is qualified by a 
tendency to variation. Like produces like, but not ex¬ 
actly. The similarity never amounts to identity. So that 
we have two opposing tendencies — the hereditary ten¬ 
dency to copy the original stock, and a distinct tendency 
to deviate from it. 


216 


COMPARATIVE ZOOLOGY. 


This is one of the most universal facts in nature. Ev¬ 
ery development ends in diversity. All know that no 
two individuals of a family, human or brute, are abso-^ 
lutely alike. There are always individual differences by 
which they can be distinguished. Evidently a parent 
does not project precisely the same line of influences upon 
each of its offspring. 

This variability makes possible an indefinite modifica¬ 
tion of the forms of life. For the variation extends to 
the whole being, even to every organ and mental char¬ 
acteristic as well as to form and color. It is very slight 
from generation to generation; but it can be accumulated 
Dy choosing from a large number of individuals those 
which possess any given variation in a marked degree, 
and breeding from these. Nature does this by the very 
gradual process of “ natural selection Man hastens it, so 
to speak, by selecting extreme varieties. Hence we have 
in our day remarkable specimens of Poultry, Cattle, and 
Hogs, differing widely from the wild races. 

Sometimes we notice that children resemble, not then 
parents, but their grandparents or remoter ancestors. This 
tendency to revert to an ancestral type is called atavism. 
Occasionally, stripes appear on the legs and shoulders of 
the Horse, in imitation of the aboriginal Horse, which was 
striped like the Zebra. Sheep have a tendency to revert 
to dark colors. 

The laws governing inheritance are unknown. No one 
can say why one peculiarity is transmitted from father to 
son, and not another; or why it appears in one member 
of the family, and not in all. Among the many causes 
which tend to modify animals after birth are the quality 
and quantity of food, amount of temperature and light, 
pressure of the atmosphere, nature of the soil or water, 
habits of fellow-animals, etc. 

Occasionally animals occur, widely different in struct* 


DEVELOPMENT. 


217 


ure 7 having a very close external resemblance. Barnacles 
were long mistaken for Mollusks, Polyzoans for Polyps, 
and Lamprey-eels for Worms. Such forms are termed 
homomorphic. 

Members of one group often put on the outward ap¬ 
pearance of allied species in the same locality: this is 
called mimicry. “ They appear like actors or masquerad¬ 
ers dressed up and painted for amusement, or like swin¬ 
dlers endeavoring to pass themselves off for well-known 
and respectable members of society.” Thus, certain But¬ 
terflies on the Amazons have such a strong odor that the 
Birds let them alone; and Butterflies of another family 
in the same region have assumed for protection the sam* 
form and color of wing. So we have bee-like Moths, 
beetle-like Crickets, wasp-like Flies, and ant-like Spiders; 
harmless and venomous Snakes copying each other, and 
Orioles departing from their usual gay coloring to imi 
tate the plumage, flight, and voice of quite another style 
of Birds. The species which are imitated are much more 
abundant than those which mimic them. There is also a 
general harmony between the colors of an animal ana 
those of its habitation. We have the white Polar Beai, 
the sand-colored Camel, and the dusky Twilight-moths. 
There are Birds and Reptiles so tinted and mottled as ex 
actly to match the rock, or ground, or bark of a tree they 
frequent; and there are Insects rightly named “Walking 
sticks” and “ Walking -leaves.” These coincidences arc 
not always accidental, but often intentional on the part o_ 
nature, for the benefit of the imitating species. Gener¬ 
ally, they wear the livery of those they live on, or ape 
the forms more favored than themselves. 

5. Homology , Analogy , and Correlation. 

The tendency to repetition in the development of ani 
mals leads to some remarkable affinities. Parts or organs, 


218 


COMPARATIVE ZOOLOGY. 


having a like origin and development, and therefore the 
same essential structure, whatever their form or function, 
are said to be homologous; while parts or organs corre¬ 
sponding in use are called analogous. By serial homol¬ 
ogy is meant the homology existing between successive 
parts of one animal. 

The following are examples of homology: the arms of 
Man, the fore-legs of a Horse, the paddles of a Whale, 
the wings of a Bird, the front flippers of a Turtle, and the 
pectoral fins of a Fish; the proboscis of a Moth, and the 
jaws of a Beetle; the shell of a Snail, and both valves of 
a Clam. The wings of the Bird, Flying Squirrel, and Bat 
are hardly homologous, since the wing of the first is de¬ 
veloped from the fore-limb only; that of the Squirrel is 
an extension of the skin between the fore and hind limbs; 
while in the Bat the skin stretches between the fingers, 
and then down the side to the tail. Examples of serial 
homology: the arms and legs of Man; the upper and 
lower set of teeth : the parts of the vertebral column, 
however modified; the scapular and pelvic arches; the 
humerus and femur; carpus and tarsus; the right and left 
sides of most Animals; the dorsal and anal fins of Fishes. 
The legs of a Lobster and Lizard, the wings of a Butter¬ 
fly and Bird, the gills of a Fish, and the lungs of other 
Vertebrates, are analogous. The air-bladder of a Fish is 
homologous with a lung, and analogous to the air-cham¬ 
bers of the Nautilus. 

In the midst of the great variety of form and structure 
in the animal world, a certain harmony reigns. Not only 
are different species so related as to suggest a descent 
from the same ancestor, but the parts of any one organ¬ 
ism are so closely connected and mutually dependent that 
the character of one must receive its stamp from the char¬ 
acter of all the rest. Thus, from a single tooth it may be 
inferred that the animal had a skeleton and spinal cord, 


DEVELOPMENT. 


219 


and that it was a carnivorous, hot-blooded Mammal. Cer¬ 
tain structures always co-exist. Animals with two occipi¬ 
tal condyles, and non - nucleated blood - corpuscles, suckle 



...■Fi 


Fie. 179. 






Fig. 182. 


HOMOLOGIES OF LIMBS. 

Fig. 179.— Arm and Leg of Man, as they are when he gets down on all-fours. Fig. 
ISO.— Fore and Hind Legs of Tapir. Fig. 181.— Fore Leg of Seal and Hind Leg 
of Alligator. Fig. 1S2.— Wing of the Bat. S, scapula; I, ilium, or shin-bone of 
pelvis; H, humerus; F, femur; O, olecranon, or tip of the elbow; P, patella; 
U, ulna; T, tibia; R, radius; Fi, Fibula; Po, pollex, or thumb; Ha, hallex, or 
great toe. Compare the fore and hind limbs of the same animal, and the fore 
or hind limbs of different animals. Note the directions of the homologous seg¬ 
ments. 














220 


COMPARATIVE ZOOLOGY. 


their young, i. e., they are Mammals. All Ruminant 
hoofed beasts have horns and cloven-feet. If the hoofs 
are even, the horns are even, as in the Ox; if odd, as in 
the Rhinoceros, the horns are odd, i. e., single, or two 
placed one behind the other. Recent creatures with feath¬ 
ers always have beaks. Pigeons with short beaks have 
small feet; and those with long beaks, large feet. The 
long limbs of the Hound are associated with a long head. 
A white spot in the forehead of a Horse generally goes 
with white feet. Hairless Dogs are deficient in teeth. 
Long wings usually accompany long tail-feathers. White 
Cats with blue eyes are usually deaf. A Sheep with nu¬ 
merous horns is likely to have long, coarse wool. Homol¬ 
ogous parts tend to vary in the same manner; if one is 
diseased, another is more likely to sympathize with it than 
one not homologous. This association of parts is called 
correlation of growth. 

6. Individuality . 

It seems at first sight very easy to define an individual 
animal. A single Fish, or Cow, or Snail, or Lobster is 
'plainly an individual; and the half of one such animal is 
plainly not one. But when we consider animals in colo¬ 
nies, like Corals, it is not so easy to say whether the indi¬ 
vidual is the colony or the single Polyp. Is the tree the 
individual, or the bud ? If we say the former—the colony 
—what shall we say to the free buds of a Hydroid colony, 
living independent lives, and scattered over square miles 
of ocean? Are they parts of one individual? If we 
choose the latter as our standard, we are in equal difficul¬ 
ty; for we must then call an individual the bud of the 
Portuguese Man-of-war, reduced to a mere bladder or 
feeler, and incapable of leading an independent life. We 
thus find it necessary to distinguish at least two kinds 
of individuals —physiological individuals , applying that 


DEVELOPMENT. 


221 


name to any animal form capable of leading an indepen¬ 
dent life; and morphological individuals , one of which is 
the total product of an egg. Such an individual may be 
a single physiological individual, as the Fish; or many 
united, as the Coral stock; or many separate physiological 
individuals, as in the Hydroids or Plant-lice. The single 
members of such a compound morphological individual 
are called zooids , or personae ,, and are found wherever 
asexual reproduction takes place. 


7. Relations of Number, Size , Form , and Rank. 

The Animal Kingdom has been likened to a pyramid, 
the species diminishing in number as they ascend in the 
scale of complexity. This is not strictly true. The num¬ 
ber of living species known is at least 300,000, of which 
more than nine tenths are Invertebrates. A late enumer¬ 
ation gives the following figures for the number of de¬ 
scribed species: 


Protozoa. 2,700 

Ccelenterata. 1,560 

Vermes. 5,580 

Arthropoda.175,100 


Echinodermata. 800 

Mollusca.20,210 

Vertebrata .25,200 


These figures are lower than those usually given. Of 
Vertebrates, Fishes are most abundant; then follow Birds, 
Mammals, Keptiles, and Amphibians. There are usually 
said to be about 200,000 species of Insects. 

The largest species usually belong to the higher classes. 
The aquatic members of a group are generally larger than 
the terrestrial, the marine than the fresh-water, and the 
land than the aerial. The extremes of size are an Infu¬ 
sorium, ts-Jutf of an inch in diameter, the smallest animal 
ever measured, and the Whale, one hundred feet long, the 
largest animal ever created. The female is sometimes 
larger than the male, as of the Nautilus, Spider, and Eagle. 
The higher the class, the more uniform the size. Of all 











222 


COMPARATIVE ZOOLOGY. 


groups of animals, Insects and Birds are the most con¬ 
stant in their dimensions. 

Every organism has its own special law of growth: a 
Fish and an Oyster, though born in the same locality, de¬ 
velop into very different forms. Yet a symmetry of plan 
underlies the structure of all animals. In the embryo, 
this symmetry of the two ends, as well as the two sides, 
is nearly perfect; but it is subsequently interfered with 
to adapt the animal to its special conditions of life. It is 
a law that an animal grows equally in those directions in 
which the incident forces are equal. The Polyp, rooted 
to the rocks, is subjected to like conditions on all sides, 
and, therefore, it has no right and left, or fore and hind 
parts. The lower forms, generally, are more or less geo¬ 
metrical figures: spheroidal, as the Sea-urchin; radiate, 
as the Star-fish; and spiral, as many Foraminifers. The 
higher animals are subjected to a greater variety of con¬ 
ditions. Thus, a Fish, always going through the water 
head foremost, must show considerable difference between 
the head and the hinder end; or a Turtle, moving over 
the ground with the same surface always down, must have 
distinct dorsal and ventral sides. 

Nevertheless, there is a striking likeness between the 
two halves or any two organs situated on opposite sides 
of an axis. And, first, a bilateral symmetry is most com¬ 
mon. It is best exhibited by the Articulates and Verte¬ 
brates, but nearly all animals can be clearly divided into 
right and left sides — in other words, they appear to be 
double. A vertical plane would divide into two equal 
parts our brain, spinal cord, vertebral column, organs of 
sight, hearing, and smell; our teeth, jaws, limbs, lungs, 
etc. In fact, the two halves of every egg are identical. 
There are many exceptions: the heart and liver of the 
higher Vertebrates are eccentric; the nervous system of 
Mollusks is scattered; the hemispheres of the human 


DEVELOPMENT. 


223 


brain are sometimes unequal; the corresponding bones in 
the right and left arms are not precisely the same length 
and weight; the Narwhal has an immense tusk on the left 
side, with none to speak of on the other; Rabbits have 
been born with one ear, and Stags with one horn; the 
Rattlesnake has but one lung; both eyes of the Flounder 
and Halibut are on the same side; the claws of the Lob¬ 
ster differ; and the valves of the Oyster are unequal. 
But all these animals and their organs are perfectly sym¬ 
metrical in the embryo state. 

Again, animals exhibit a certain correspondence be¬ 
tween the fore and hind parts. 121 Thus, the two ends of 
the Centipede repeat each other. Indeed, in some Worms, 
the eyes are developed in the last segment as well as the 
first. So a Vertebrate may be considered not only as two 
individuals placed side by side, but also as two individu¬ 
als put end to end—the head and arms representing one, 
and the legs the other. In the embryo of Quadrupeds, 
the four limbs are closely alike. But in the adult, the 
fore and hind limbs differ more than the right and left 
limbs, because the functions are more dissimilar. An ex¬ 
treme want of symmetry is seen in Birds which combine 
aerial and land locomotion. 

There is also a tendency to a vertical symmetry , of 
up-and-down arrangement — the part above a horizontal 
plane being a reversed copy of the part below. A good 
example is the posterior half of a Cod, while the tail of a 
Shark shows the want of it. This symmetry decreases as 
we ascend the scale. In most animals there is consider¬ 
able difference between the dorsal and ventral surfaces; 
and in all the nervous system is more symmetrically dis¬ 
posed than the digestive. 

Every animal is perfect in its kind and in its place. 
Yet we recognize a gradation of life. Some animals are 
manifestly superior to some others. But it is not so easy 


224 


COMPARATIVE ZOOLOGY. 


to say precisely what shall guide us in assorting living 
forms into high and low. Shall we make structure the 
criterion of rank? Plainly the simple Jelly-fish is be¬ 
neath complicated Man. An ounce of muscle is worth a 
pound of protoplasm, and a grain of nervous matter is of 
more account than a ton of flesh. The intricate and fin¬ 
ished build of the Horse elevates him immeasurably above 
the stupid Snail. The repetition of similar parts, as in the 
Worm, is a sign of low life. So also a prolonged posterior 
is a mark of inferiority, as the Lobsters are lower than the 
Crabs, Snakes than Lizards, Monkeys than Apes. The 
possession of a head distinct from the region behind 
it is a sign of power. And in proportion as the fore¬ 
limbs are used for head purposes, the animal ascends 
the scale: compare the Whale, Horse, Cat, Monkey, and 
Man. 

But shall the Fish, never rising above the “ monotony 
of its daily swim,” be allowed to outrank the skilful Bee? 
Shall the brainless, sightless, almost heartless Amphioxus, 
a Vertebrate, be allowed to stand nearer to Man than the 
Ant? What is the possession of a backbone to intelli¬ 
gence? Ho good reason can be given why we might not 
be just as intelligent beings if we carried, like the Insect, 
our hearts in our backs and our spinal cords in our breasts. 
.So far as its activity is concerned, the brain may be as ef¬ 
fective if spread out like a map as packed into its present 
shape. Even animals of the same type, as Vertebrates, 
cannot be.ranked according to complexity. For while 
Mammals, on the whole, are superior to Birds, Birds to 
Reptiles, and Reptiles to Fishes, they are not so in every 
respect. Man himself is not altogether at the head of 
creation. We carry about in our bodies embryonic struct¬ 
ures. That structural affinity and vital dignity are not 
always parallel may be seen by comparing an Australian 
and an Englishman. 128 


DEVELOPMENT. 


225 


Function is the test of worth. Hot mere work, how¬ 
ever; for we must consider its quality and scope. An 
animal may be said to be more perfect in proportion as 
its relations to the external world are more varied, pre¬ 
cise, and fitting. Complexity of organization, variety, 
and amount of power are secondary to the degree in 
which the whole organism is adapted to the circumstances 
which surround it, and to the work which it has to do. 
Ascent in the animal scale is not a passage from animals 
with simple organs to animals witli complex organs, but 
from simple individuals with organs of complex function 
to complex individuals with organs of simple function : 
the addition as we ascend being not function, but of parts 
to discharge those functions; and the advantage gained, 
not another thing done, but the same thing done better. 
Advance in rank is exhibited, not by the possession of 
more life (for some animalcules are ten times more lively 
than the busiest Man), but by the setting apart of more 
organs for special purposes. The higher the animal, the 
greater the number of parts combining to perform each 
function. The power is increased by this division of la¬ 
bor. The most important feature in this specialization is 
the tendency to concentrate the nervous energy towards 
the head ( capitalization ). It increases as we pass from 
lower to higher animals. 

As a rule, fixed species are inferior to the free, water 
species to land species, fresh-water animals to marine, arc¬ 
tic forms to tropical, and the herbivorous to the carniv¬ 
orous. Precocity is a sign of inferiority: compare the 
chicks of the Hen and the Robin, a Colt with a Kitten, 
the comparatively well - developed Caterpillar with the 
footless grub of the Bee. Among Invertebrates, the male 
is frequently inferior, not only in size, but also in grade 
of organization. Animals having a wide range as to cli- 

15 


226 


COMPARATIVE ZOOLOGY. 


mate, altitude, or depth are commonly inferior to those 
more restricted: Man is a notable exception. 

There is some relation between the duration of life and 
the size, structure, and rank of animals. Vertebrates not 
only grow to a greater size, but also live longer than In¬ 
vertebrates. Whales and Elephants are the longest-lived; 
and Falcons, Ravefis, Parrots and Geese, Alligators and 
Turtles, and Sharks and Pikes, are said to live a century. 
The life of Quadrupeds generally reaches its limit when 
the molar teeth are worn down: those of the Sheep last 
about 15 years; of the Ox, 20; of the Horse, 40; of the 
Elephant, 100. Many inferior species die as soon as they 
have laid their eggs, just as herbs perish as soon as they 
have flowered. 


8. The Struggle for Life. 

Every species of animal is striving to increase in a geo¬ 
metrical ratio. But each lives, if at all, by a struggle at 
some period of its life. The meekest creatures must fight, 
or die. 

“ There is no exception to the rule that every organic 
being naturally increases at so high a rate that, if not de¬ 
stroyed, the earth would soon be covered by the progeny 
of a single pair.” If the increase of the human race were 
not checked, there would not be standing-room for the 
descendants of Adam and Eve. A pair of Elephants, the 
slowest breeder of all known animals, would become the 
progenitors, in seven and one half centuries, of 19,000,000 
of Elephants, if death did not interfere. Evidently a vast 
number of young animals must perish while immature, 
and a far greater host of eggs fail to mature. A single 
Cod, laying millions of eggs, if allowed to have its own 
way, would soon pack the ocean. 

Yet, so nicely balanced are the forces of nature, the 
average number of each kind remains about the same. 


DEVELOPMENT. 


227 


The total extinction of any one species is exceedingly 
rare. The number of any given species is not determined 
by the number of eggs produced, but by its conditions. 123 
Aquatic birds outnumber the land birds, because their 
food never fails, not because they are more prolific. The 
Fulmar-petrel lays but one egg, yet it is believed to be 
the most numerous bird in the world. 

The main checks to the high rate of increase are: cli¬ 
mate (temperature and moisture), acting directly or indi¬ 
rectly by reducing food; and other animals , either rivals 
requiring the same food and locality, or enemies, for the 
vast majority of animals are carnivorous. Offspring are 
continually varying from their parents, for better or worse. 
If feebly adapted to the conditions of existence, they will 
finally go to the wall. But those forms having the slight¬ 
est advantage over others inhabiting the same region, 
being hardier or stronger, more agile or sagacious, will 
survive. Should this advantageous variation become 
hereditary and intensified, the new variety will gradually 
extirpate or replace other kinds. This is what Mr. Dar¬ 
win means by Natural Selection, and Herbert Spencer by 
the Survival of the Fittest 































4 







« 








SYSTEMATIC ZOOLOGY. 


Facts are stupid things until brought into connection with some general 
law.—A gassiz. 

No man becomes a proficient in any science who does not transcend sys¬ 
tem, and gather up new truth for himself in the boundless field of research. 
—Dr. A. P. Peabody. 

Never ask a question if you can help it; and never iet a thing go un« 
known for the lack of asking a question if you can’t help it.— Beecher. 

He is a thoroughly good naturalist who knows his own parish thoroughly. 
—Charles Kingsley. 


THE CLASSIFICATION OF ANIMALS. 


231 


CHAPTER XXL 

THE CLASSIFICATION OF ANIMALS. 

The Kingdom of Nature is a literal Kingdom. Order 
and beaut} r , law and dependence, are seen everywhere. 
Amidst the great diversity of the forms of life, there is 
unity; and this suggests that there is one general plan, 
but carried out in a variety of ways. 

Naturalists have ceased to believe that each animal or 
group is a distinct, circumscribed idea. “Every animal 
has a something in common with all its fellows: much 
with many of them; more with a few; and, usually, so 
much with several, that it differs but little from them.” 
The object of classification is to bring together the like, 
and to separate the unlike. But how shall this be done? 
To arrange a library in alphabetical order, or according to 
size, binding, date, or language, would be unsatisfactory. 
We must be guided by some internal character. We must 
decide whether a book is poetry or prose; if poetry, 
whether dramatic, epic, lyric, or satiric; if prose, whether 
history, philosophy, theology, philology, science, fiction, 
or essay. The more we subdivide these groups, the more 
difficult the analysis. 

A classification of animals, founded on external resem¬ 
blances—as size, color, or adaptation to similar habits of 
life—would be worthless. It would bring together Fish¬ 
es and Whales, Birds and Bats, Worms and Eels. Nor 
should it be based on any one character, as the quality 
of the blood, structure of the heart, development of the 
brain, embryo-life, etc.; for no character is of equal value 
in every tribe. A natural classification must rest on those 


232 


COMPARATIVE ZOOLOGY. 


prevailing characters which are the most constant.™ And 
sucli a classification cannot be linear. It is impossible to 
arrange all animal forms from the Sponge to Man in a 
single line, like the steps of a ladder, according to rank. 
Nature passes in so many ways from one type to another, 
and so multiplied are the relations between animals, that 
one series is out of the question. There is a number of 
series, and series within series, sometimes proceeding in 
parallel lines, but more often divergent. The animals ar¬ 
range themselves in radiating groups, each group being 
connected, not with two groups merely, one above and the 
other below, but with several. Life has been likened to a 
great tree with countless branches spreading widely from 
a common trunk, and deriving their origin from a com¬ 
mon root; branches bearing all manner of flowers, every 
fashion of leaves, and all kinds of fruit, and these for 
every use. 

The groups into which we are able to cast the various 
forms of animal development are very unequal and dis¬ 
similar. We must remember that a genus, order, or class 
is not of equal value throughout the kingdom. Moreover, 
each division is allied to others in different degrees—the 
distance between any two being the measure of that'affin¬ 
ity. The lines between some are sharp and clear, between 
others indefinite. Like the islands of an archipelago, some 
groups merge into one another through connecting reefs, 
others are sharply separated by unfathomable seas, yet all 
have one common basis. Links have been found reveal¬ 
ing a relationship, near or distant, even between animals 
whose forms are very unlike. There are Fishes ( Dipnoi) 
with some Amphibian characters, and fish-like Amphibi¬ 
ans (Axolotl). The Ichthyosaurus is a Lizard with fish- 
characteristics. Birds seem isolated, but they are closely 
connected with Keptiles by fossil forms. Even the great 
gap in the Animal Kingdom—that separating Vertebrates 


THE CLASSIFICATION OF ANIMALS. 


233 


and Invertebrates — is partially bridged on the one side 
by Amphioxus, and on the other by the Tunicates. 

We have, then, groups subordinate to groups, and inter¬ 
locking, but not representing so many successive degrees 
of organization. For, as already intimated, complication 
of structure does not rise in continuous gradation from 
one group to another. Every type starts at a lower point 
than that at which the preceding class closes; so that the 
lines overlap. While one class, as a whole, is higher than 
another, some members of the higher class may be infe¬ 
rior to some members of the lower one. Thus, certain 
Star-fishes are nobler than certain Mollusks; the Nautilus 
is above the Worm, and the Bee is more worthy than the 
lowest Fish. The groups coalesce by their inferior or less 
specialized members; e. y., the Fishes do not graduate into 
Amphibians through their highest forms, but the two come 
closest together low down in the scale. Man appears to 
be the goal of creation; but even within the Vertebrate 
series, every step of development, say of the Fish, is away 
from the goal. The highest Fish is the one farthest from 
Man. 

A number of animals may, therefore, have the same 
grade of development, but conform to entirely different 
types. While a fundamental unity underlies the whole 
Animal Kingdom, suggesting a common starting-point, we 
recognize several distinct plans of structure. 125 Animals 
like the Amoeba, with no cellular tissues nor true eggs, 
form the subkingdom Protozoa. Animals like the Sponge, 
with independent cells, one excurrent and many incurrent 
openings, form the subkingdom Spongida. Animals like 
the Coral, unlike all others, have an alimentary canal but 
no body-cavity, have no separate nervous and vascular 
regions, and the parts of the body radiate from a centre. 
Such form a subkingdom called Coelenterata. Animals 
like the Star-fish, having also a radiating body, but a closed 


234 


COMPARATIVE ZOOLOGY. 


alimentary canal, and a distinct symmetrical nervous sys¬ 
tem, constitute the subkingdom Echinodermata , 126 Ani¬ 
mals like the Angle-worm, bilaterally symmetrical, one- 
jointed, or composed of joints following each other from 
front to rear, with no jointed limbs, constitute the sub¬ 
kingdom Vermes. Animals like the Snail, with a soft, 
unjointed body, a mantle, a foot, a two or three cham¬ 
bered heart, and a nervous system in the form of a ring 
around the gullet, constitute the subkingdom Mollusca. 
Animals like the Bee, with a jointed body and jointed 
limbs, form the subkingdom Arthropoda. Animals like 
the Sea-squirts, sack or barrel shaped, with a mantle cav¬ 
ity penetrated by an excurrent and an incurrent opening, 
with heart and gills, form the subkingdom Tunicata. An¬ 
imals like the Ox, having a double nervous system, one 
(the sympathetic) lying on the upper side of the aliment¬ 
ary canal, the other and main part (spinal) lying along the 
back, and completely shut off from the other organs by a 
partition of bone or gristle, known as the “ vertebral col¬ 
umn,and having limbs, never more than four, always on 
the side opposite the great nervous cord, constitute the 
subkingdom Vertebrata. 

Comparing these great divisions, we see that the Verte¬ 
brates differ from all the others chiefly in having a double 
body-cavity and a double nervous system, the latter lying 
above the alimentary canal; while Invertebrates have one 
cavity and one nervous system, the latter being placed 
either below or around the alimentary canal. The Vermes 
are closely related to all the following subkingdoms of 
Invertebrates, most nearly to Mollusks and Tunicates, 
while the latter have affinities with the Vertebrates. The 
Echinoderms and Ccelenterates are built on the common 
type of a star; but they differ from each other in the 
presence or absence of distinct alimentary, circulatory, 
and nervous systems. 


THE CLASSIFICATION OF ANIMALS. 235 

But there are types within types. Thus, there are five 
modifications of the Vertebrate type —Fish, Amphibian, 
Reptile, Bird, and Mammal; and these are again divided 
and subdivided, for Mammals, e. y., differ among them¬ 
selves. So that in the end we have a constellation of 
groups within groups, founded on peculiar characters of 
less and less importance, as we descend from the general 
to the special. 

Individuals are the units of the Animal Creation. An 
animal existence, complete in all its parts, is an individual, 
whether separate, as Man, or living in a community, as the 
Coral. w 

Species is the smallest group of individuals which can 
be defined by distinct characteristics, and which is sepa¬ 
rated by a gap from all other like groups. A well-marked 
subdivision of a species is called a variety. Crosses be¬ 
tween species are called hybrids , as the Mule. 

G-enus is a group of species having the same essential 
structure. Thus, the closely allied species Cat, Tiger, and 
Lion belong to one genus. 

Family, or Tribe, is a group of genera having a simi¬ 
lar form. Thus, the Dogs and Foxes belong to different 
genera, but betray a family likeness. 

Order is a group of families, or genera, related to one 
another by a common structure. Cats, Dogs, Hyenas, and 
Bears are linked together by important anatomical features; 
their teeth, stomachs, and claws show carnivorous habits. 

Class is a still larger group, comprising all animals 
which agree simply in a special modification of the type 
to which they belong. Thus, Fishes, Amphibians, Rep¬ 
tiles, Birds, and Mammals are so many aspects of the Ver¬ 
tebrate type. 

Subkingdom is a primary division of the Animal King¬ 
dom, which includes all animals formed upon one of the 
various types of structure; as Vertebrate. 


236 


COMPARATIVE ZOOLOGY. 


The subkingdoms are grouped into two great Series, 
according to their histological structure and mode of de¬ 
velopment. 128 

These terms were invented bj Linnaeus, except Family, 
Subkingdom, and Series. To Linnaeus we are also in¬ 
debted for a scientific method of naming animals. Thus, 
a Dog, in Zoology, is called Canis familiaris , which is the 
union of a generic and a specific name, corresponding to 
the surname and the Christian name in George Washing¬ 
ton, only the specific name comes last. It will be under¬ 
stood that these are abstract terms, expressing simply the 
relations of resemblance: there is no such thing as genus 
or species. 

Classification is a process of comparison. He is the 
best naturalist who most readily and correctly recognizes 
likeness founded on structural characters. As it is easier 
to detect differences than resemblances, it is much easier 
to distinguish the class to which an animal belongs than 
the genus, and the genus than the species. In passing 
from species to classes, the characters of agreement be¬ 
come fewer and fewer, while the distinctions are more 
and more manifest; so that animals of the same class are 
more like than unlike, while members of distinct classes 
are more unlike than like. 

To illustrate the method of zoological analysis by search¬ 
ing for affinities and differences, we will take an example 
suggested by Professor Agassiz. Suppose we see together 
a Dog, a Cat, a Bear, a Horse, a Cow, and a Deer. The 
first feature which strikes us as common to any two of 
them is the horn in the Cow and the Deer. But how 
shall we associate either of the others with these ? We 
examine the teeth, and find those of the Dog, the Cat, and 
the Bear sharp and cutting; while those of the Cow, the 
Deer, and the Horse have flat surfaces, adapted to grind¬ 
ing and chewing, rather than to cutting and tearing. We 


THE CLASSIFICATION uF ANIMALS. *237 

compare these features of their structure with the habits 
of these animals, and find that the first are carnivorous— 
that they seize and tear their prey; while the others are 
herbivorous, or grazing, animals, living only on vegetable 
substances, which they chew and grind. We compare, 
further, the Horse and Cow, and find that the Horse has 
front teeth both in the upper and the lower jaw, while 
the Cow has them only in the lower; and going still 
further, and comparing the internal with the external 
features, we find this arrangement of the teeth in direct 
relation to the different structure of the stomach in the 
two animals—the Cow having a stomach with four pouch¬ 
es, while the Horse has a simple stomach. Comparing 
the Cow and Deer, we find the digestive apparatus the 
same in both; but though both have horns, those of the 
Cow are hollow, and last through life; while those of the 
Deer are solid, and are shed every year. Looking at the 
feet, we see that the herbivorous animals are hoofed; the 
carnivorous, clawed. The Cow and Deer have cloven 
feet, and are ruminants; the Horse has a single hoof, and 
does not chew the cud. The Dog and Cat walk on the 
tips of their fingers and toes (digitigrade); the Bear treads 
on the palms and soles (plantigrade). The claws of the 
Cat are retractile; those of the Dog and Bear are fixed. 

In this way we determine the exact place of 6aeh ani¬ 
mal. The Dog belongs to the kingdom Animalia , sub¬ 
kingdom Vertebrate class Mammalia , order Carnivora , 
family Canidce , genus Canis , species Familiar is, variety 
Hound (it may be), and its individual name, perhaps, is 
“Rover.” The Cat differs in belonging to the family 
Felidoe , genus Felis, species Catus. The Bear belongs to 
the family Ursidce , genus Ursus , and species Ferox , if 
the Grizzly is meant. The Horse, Cow, and Deer belong 
to the order Ungulata ; but the Horse is of the family 
Equidoe , genus Equus , species Caballus; the Cow is of 


COMPARATIVE ZOOLOGY. 


238 

the family Bovidce, genus Bos, species Taurus; the Deer 
is of the family Cervidce, genus Cervus, species Virgini- 
anus, if the common Deer is meant. 

The diagram on the opposite page roughly represents 
(for the relations of animals cannot be expressed on a 
plane surface) the relative positions of the subkingdoms 
and classes according to affinity and rank * 

SERIES I.—PROTOZOA. 

Animals without cellular tissues, and with no true eggs. 
The body which corresponds to the egg does not develop 
a blastoderm. 


Subkingdom.— Protozoa. 

This division was proposed by Yon Siebold in 1845, to 
contain that vast cloud of microscopic beings on the verge 
of the Animal Kingdom which could not be received into 
the other subkingdoms. It is artificial and provisional. 
The classes composing it are not founded on a common 
type, but are distinguished by the absence rather than the 
presence of positive characters. Many stand parallel to 
the Protopkyta of the Vegetable World, and no definite 
line can be drawn between them. 

Protozoans agree in being minute, aquatic, and exceed¬ 
ingly simple in structure, their bodies consisting mainly 
or wholly of the contractile, gelatinous matter called pro¬ 
toplasm, or sarcode — the first homogeneous substance 
which has the power of controlling chemical and physical 
forces. They have no cellular organs or tissues, yet they 
take and assimilate food, grow, and multiply, which are 


* The student should master the distinctions between the great groups, or 
classes, before proceeding to a minuter classification. “The essential mat¬ 
ter, in the first place,” says Huxley, “is to be quite clear about the different 
classes, and to have a distinct knowledge of all the sharply definable modifi¬ 
cations of animal structure which are discernible in the Animal Kingdom.” 



THE CLASSIFICATION OF ANIMALS. 


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240 


COMPARATIVE ZOOLOGY. 


the essential signs of life. The usual methods of repro¬ 
duction are self-division and budding. 

The subkingdom may be divided into four classes: 2£o- 
nera , Gregarinida , Rhizopoda , and Infusoria. 


Class I.— Monera. 

These simplest living beings are organless 
bits of protoplasma, with no distinction of 
layers, round when at rest, and with pseu¬ 
dopodia when active. They are all aquatic, 
fig. 183. -Pro- and some are parasitic. Such is Protamoeba, 
Fig. 183. 



tamceba pri¬ 
mitive. 


Class II.— Gregarinida. 

The Gregarinae, discovered by Dufour in 1828, are 
among the simplest animal forms of which we have any 
knowledge. They closely resemble a cell, or microscopic 
egg; the only organ is a nucleus, suspended in extremely 
mobile granular matter; and the most conspicuous signs 



Fig. 184 .—Gregarina gigantea, highly magnified: a, nucleus. 

of life are the contraction and lengthening of the worm- 
like body. They feed by absorption, and are all parasites, 
living in the alimentary canal of higher animals; as in 
the Cockroach, Earth-worm, and Lobster. The name is 
derived from the fact that they occur in large numbers 
crowded together. 


Class III. —Rhizopoda. 

The Rhizopods are characterized by the power of throw¬ 
ing out at will delicate processes of their bodies, called 
pseudopodia , or false feet, for prehension or locomotion. 











PKOTOZOA. 


241 


They possess no cilia. The representative forms are Amosr 
bee, Foraminifer a, and Polycystina. 

An Amoeba is a naked fresh-water Rhizopod; an in¬ 
definite bit of protoplasm, as structureless as a speck of 
jelly, save that it is made of 
two distinct layers, and has a 
nucleus and a contractile cav¬ 
ity inside. It thus differs 
from the Monera. It has no 
particular form, as it changes 
continually. It moves by put¬ 
ting forth short, blunt proc¬ 
esses, and eats by wrapping 
its body around the particle of food. The size ranges 
from -Jg- to -g feVo of an inch in diameter. Specimens can 
be obtained by scraping the mucous matter from the 
stems and leaves in stagnant ponds. 

A Foraminifer differs from an Amoeba in having an 
apparently simpler body, the protoplasm being without 
layers or cavity; its pseudopodia are long and thread-like, 
and may unite where they touch each other. It has the 
property of secreting an envelope, usually of carbonate of 



Fig. 1S5 .—Aviceba princeps, X 150; the 

same animal in various shapes. 



Fig. 186.—Rhizopods: a, a monothalamous, or single-chambered, Foraminifer (Lo- 
gena striata ); 6, a polythalamous, or many-chambered, Foraminifer (Polystomella 
crispa), with pseudopodia extended; c, a Radiolarian, one of the Polycystines 
(PodoeyrtU Schomburgkii ). 


16 







242 


COMPAKATIVE ZOOLOGY. 


lime. The shell thus formed is sometimes of extraordi¬ 
nary complexity and singular beauty. It is generally per¬ 
forated by innumerable minute orifices [foramina) through 
which the animal protrudes its myriad of glairy, thread¬ 
like arms. The majority are compound, resembling cham¬ 
bered shells, formed by a process of budding, the new 
cells being added so as to make a straight series, a spiral, 
or a flat coil. As a rule, the many-chambered species 
have calcareous, perforated shells; and the one-chambered 
have an imperforated membranous, porcelaneous, or are¬ 
naceous envelope. The former are marine. There are 
few parts of the ocean where these microscopic shells do 
not occur, and in astounding numbers. A single ounce 
of sand from the Antilles was calculated to contain over 
three millions. The bottom of the ocean, up to about 50° 
on each side of the Equator, and at depths not greater than 
2400 fathoms, is covered with the skeletons of these ani¬ 
mals, which are constantly falling upon it ( globigerina - 
ooze). Their remains constitute a great proportion of the 
so-called sand-banks which block up many harbors. Yet 
they are the descendants of an ancestry still more prolific; 
for the Foraminifera are among the most important rock¬ 
building animals. The chalk-cliffs of England, the build¬ 
ing-stone of Paris, and the blocks in the Pyramids of 
Egypt are largely composed of extinct Foraminifers. Fo¬ 
raminifera are both marine and fresh-water, chiefly marine. 

A Polycystine differs from a Foraminifer in secreting 
a siliceous, instead of a calcareous, shell, studded with 
spines; and the central part of the body is made up of 
many cells, and surrounded by a strong membrane. They 
are also more minute, but as widely diffused. They enter 
largely into the formation of some strata of the earth’s 
crust, and abound especially in the rocks of Barbadoes and 
at Richmond, Ya. The living forms are mostly marine, 
but some are fresh-water. 


PROTOZOA. 


243 



Fig. 187.— A Compound Monad 
( Uvella ), X 1000. 


Class IV. —Infusoria. 

This unassorted group of living particles derived its 
name from the fact that they were first discovered in veg¬ 
etable infusions. Every drop of 
a stagnant pool is crowded with 
them. They are all single and 
microscopic, yet of various -sizes, 
the difference between the small¬ 
est and largest being greater than 
the difference between a Mouse 
and an Elephant. Some are fixed 
(as Vorticella ), but the majority are free, and constantly 
in motion, propelled by countless cilia, as a galley by its 
oars. The delicate body consists of two 
layers of sarcode (there are no cellular 
tissues, but the whole body represents a 
single cell), covered by a membrane, or 
skin, having one or two contractile cavi¬ 
ties, and a nucleus. Food-granules can 
often be seen. On one side is a slight 
depression, or “ mouth,” leading to a 
short, funnel-shaped throat. A mouth 
and a rudimentary digestive cavity are 
among the distinctive features of these 
Protozoans. Some have a pigment-speck 
—the simplest sense organ—and in the 
stem of Vorticella the first rudiments of 
muscle may be found. They multiply so rapidly (chiefly 
by self-division), that a Paramecium , the most common 
form, may become the parent of 1,364,000 in forty-two days. 

There are two main groups: Flagellata , or Monads, 
provided with one or two flagella, or long, bristle-like 
cilia; and Ciliata , which are furnished with numerous 
vibratile cilia. 



(Paramecium, aurelia), 
X 300: m , mouth ; v, 
contractile vesicles; n, 
nucleus. 




244 


COMPARATIVE ZOOLOGY. 


SERIES II.—METAZOA. 

The Metazoa include all those animals which reproduce 
by true eggs and spermatozoa, whose germ develops a 
blastoderm, and which have cellular tissues. There are 
seven subkingdoms. 

Subkingdom I.—Spongida. 

The position of the Sponges has been much disputed. 
At first they were thought to be on the border-line be¬ 
tween animals and plants, and were assigned by some to 
the animals and by others to the vegetables. Later, and 
up to very recent years, they were assigned to the Proto¬ 
zoa. The discovery of their mode of reproduction and 
development has determined that they belong to the 
Metazoa. 

The Sponges are formed of an aggregate of membrane¬ 
less amoeboid or ciliated cells. They usually have a skele¬ 
ton, which may be calcareous, horny, or siliceous. They 
have a central cavity, with numerous incurrent orifices 
and one excurrent opening. They reproduce by true 
eggs, as well as by budding and fission. 

The cells of the Sponge are relatively independent, 
whence they have been regarded as colonies of amoeboid 
animals, and by some naturalists are still so considered. 




SPONGIDA. 


245 


They develop, however, regularly from the egg, and the 
cells acquire their independence only at a late date in de¬ 
velopment. Some of the cells gain cilia, or flagella, and 
drive the water through numerous channels into the cen¬ 
tral cavity, whence it is discharged by one opening. Each 
cell of the Sponge feeds itself from the particles con¬ 
tained in the water. 

The Sponge-individual consists of one exhalant orifice, 
with the channels leading into it. An ordinary bathing- 



Fig. 190.—Horny Skeleton of a Sponge. 


sponge constitutes a colony of such individuals, which are 
not definitely marked off from each other. Other Sponges 
have only one osculum, and such are a single individual. 

Some few Sponges have no skeleton. Most have one 
of horny fibres, strengthened with siliceous spicules. These 
last are absent in the commercial Sponges, and in them 
the horny fibres are much tougher than in most Sponges. 



246 


COMPARATIVE ZOOLOGY. 


A few Sponges, as the Venus’s Flower-basket ( Euplec - 
telld), have siliceous and others have calcareous skeletons. 

Excepting a few small fresh-water species (as Spon- 
gilla), Sponges are marine. In the former, the cellular 
part is greenish, containing chlorophyll; in the latter, it 
is brown, red, or purple. In preparing the Sponge of 
commerce, this is rotted by exposure, and washed out. 
The best fishing-grounds are the eastern end of the Medi¬ 
terranean and around the Bahama Islands. 

Subkingdom II.—Ccelenterata. 

These radiate animals are distinguished by having a dis¬ 
tinct cavity, whose walls have, at least, two layers of cel¬ 
lular tissue, an outer ( ectoderm ) and inner ( endoderm ), and 
usually a middle layer {mesoderm). They have thread cells, 
minute sacs containing a fluid, and connected with barbed 
filaments capable of being thrown out for stinging pur¬ 
poses. Most are provided with hollow tentacles around 
the mouth. All are aquatic, and nearly all are marine. 
There are two classes, represented by the Hydra and Sea- 
anemone. Both reproduce by budding and by eggs. 

Class I.— Hydrozoa. 

These Coelenterates have no separate digestive sac, so 
that the body is a simple tube, or cavity, into which the 
mouth opens. The nervous system is slightly developed. 
Such are the fresh-water Hydra and the oceanic Jelly-fish 
{Acaleph or Medusa). 

The body of the Hydra is tubular, soft, and sensitive, 
of a greenish or reddish color, and seldom over half an 
inch long. It is found spontaneously attached by one 
end to submerged plants, while the free end contains the 
orifice, or mouth, crowned with tentacles, by which the 
creature feeds and creeps. The body-wall consists of two 
cellular layers—ectoderm and endoderm. These surround 





CCELENTE R AT A. 


247 


a central cavity with one 
opening. The animal 
may be compared to a 
bag with a two-layered 
wall, andtentacles around 
the opening. It buds, 
and also reproduces by 
eggs. The buds, when 
adult, become detached 
from the parent. 

In most of the other 
Hydroids the colony is 
permanent, and support¬ 
ed by a horny skeleton. 
There are two kinds of 
Polyps in each colony, 
one for feeding and the 


5 



Fig. 191.—Hydra: 2, with tentacles fully extend¬ 
ed ; 3, creeping; 5, budding. 


other for reproduction. 



Fig. 192.—Hydroid ( Sertularia ) growing on a Shell. 


Sometimes the reproductive 
Polyps are separated 
from the stock in the 
form of little Jelly¬ 
fishes. The larger 
Jelly - fishes belong 
to another group 
—the Acalephce — 
and are produced as 
told on page 212. 

The Jelly-fish has 
a soft, gelatinous, 
semi-transparent,bell¬ 
shaped body, with 
tubes radiating from 
the central cavity to 
the circumference, 
and with the margin 





Fig. 193.—Jelly-fish (Pelagia noctiluca). Mediter- Fig. 194.—Portuguese Man- 

rauean. of-war ( Physalia ), ^ natu¬ 

ral size. Tropical Atlantic. 



Fig. 195—Jelly-fish (Aurelia aurita), with young m various stages. 






































CCELENTERATA. 


249 


fringed with tentacles, furnished with stinging thread- 


cells. The radiating parts are in 
Around the rim are minute colored 
spots, the “ eye - specks.” In fine 
weather, these “ sea - blubbers ” are 
seen floating on the sea, mouth down¬ 
ward, moving about by flapping their 
sides, like the opening and shutting 
of an umbrella, with great regular¬ 
ity. They are frequently phospho¬ 
rescent when disturbed. Some are 
quite small, resembling little glass 
bells; the common Aurelia is over a 


foot in diameter when full-grown ; Fiq>196j _, 


multiples of four. 



■A Medusa, seen in 
profile and from below, 
showing central polypite, 
radiating and marginal 
canals. 


while the Cyanea , the giant among 
Jelly-fishes, sometimes measures eight 
feet in diameter, with tentacles one 
hundred feet long. When dried, nothing is left but a 
film of membrane weighing only a few grains. 

There are two representative types: the Lucernaria , 
the Umbrella-acaleph, having a short pedicel on the back 
, for attachment; tentacles 

W* ««•*. disposed in eight groups 
around the margin, the 
eight points alternating 
with the four partitions 
of the body-cavity and 
the four corners of the 
mouth; not less than 
eight radiating canals, 
and no membranous veil. The common species on the 
Atlantic shore, generally found attached to eel-grass, is an 
inch in diameter, of a green color. Diseophora , the ordi¬ 
nary Jelly-fish, is free and oceanic. It differs from the 
Lucernaria in its usually larger size and solid disk, four 



Fig. 19T .—Lucernaria auricula attached to a 
piece of sea-weed; natural size. The one on 
the right is abnormal, having a ninth tuft of 
tentacles. 





COMPARATIVE ZOOLOGY. 


250 

radiating canals, which ramify and open into a circular 
vessel, and a u veil,” or shelf, always running around the 
mouth of the disk. 129 


Class II.— Anthozoa. 




These marine animals, which by their gay tentacles con¬ 
vert the bed of the ocean into a flower-garden, or by their 
secretions build up coral-islands, 
have a body like a cylindrical 
gelatinous bag. One end, the 
base, is usually attached ; the 
other has the mouth in the cen¬ 
tre, surrounded by numerous 
hollow tentacles, which are cov¬ 
ered w T ith nettling lasso-cells. 
This upper edge is turned in so 
™ . * , o .. ,. as to form a sac within a sac, 

Fig. 198.—Horizontal Section of Ac- < ’ 

tinia through the stomach, show- like the neck of a bottle turned 
iug septa and compartments. . . . 

outside in. I he inner sac, winch 
is the digestive cavity, does not reach the bottom, but 
opens into the general body-cavity. 130 The space between 
these two concentric 
tubes is divided by a 
series of vertical parti¬ 
tions, some of which 
extend from the body- 
wall to the digestive 
sac, but others fall 
short of it. Instead, 
therefore, of the radi¬ 
ating tubes of the Aca- 
lepli, there are radiat¬ 
ing spaces. No mem¬ 
bers of this class are 

. . . .. Fi<». 199.—Actinia expanded, seen from above, 

microscopic. All are showing mouth. 





CCELENTERATA. 


251 


long-lived compared with the Hydrozoa, living for several 
years. One kept in aquaria in England is now more than 
sixty years old. 

1. Soft-bodied Polyps.—The best-known representa¬ 
tive of this group is the Actinia , or Sea-anemone. It 
leads a single life, and is capable of a slow locomotion. 
Muscular fibres run around the body, and others cross 
these at right angles. The tentacles, which often number 
over two hundred, and the partitions, which are in reality 
double, are in multiples of six. At night, or when alarmed, 
the tentacles are drawn in, and the aperture firmly closed, 
so that the animal looks like a rounded lump of fleshy 
substance plastered on the rock. It feeds on Crabs and 
Mollusks. It abounds on every shore, especially of trop¬ 
ical seas. The size varies from one eighth of an inch to a 
foot in diameter. 

2. Coral Polyps.—The majority of Anthozoa secrete 
a calcareous or horny framework called “ coral.” With 
few exceptions, they are fixed 
and composite, living in colonies 
formed by a continuous process 
of budding. Their structures take 
a variety of shapes: often dome¬ 
like, but often imitating shrub¬ 
bery and clusters of leaves. The 
members of a coral community 
are organically connected; each 
feeds himself, yet is not indepen¬ 
dent of the rest. We can speak 
of the individual Corals, a , 5, c , 
but we must write them down 
abc. The compound mass is “like Fig. 200 .— organ-pipe corauruw. 

,. . . . . . pora mu8ica). Indian Ocean. 

a living sheet of animal matter, 

fed and nourished by numerous mouths and as many 
stomachs.” Life and death go on together, the old 




252 


COMPARATIVE ZOOLOGY. 


Polyps dying below as new ones are developed above. The 
living part of an Astrcea is only half an inch thick. The 
growth of the branching Madrepore is about three inches 
a year. The prevailing color of the Coral Polyps is 
green; and the usual size varies from that of a pin’s head 
to half an inch, but the Mushroom-coral (which is a single 
individual) may be a foot in diameter. 

Corals are of two kinds: those deposited within the tis¬ 
sues of the animal ( sclerodermic ), and those secreted by 
the outer surface at the foot of the Polyp ( sclerobasic ). 
The Polyps producing the former are Actinoid, resem¬ 
bling the Actinia in structure. 131 The skeleton of a single 
Polyp (called corallite, Fig. 95) is a copy of the animal, 
except the stomach and tentacles, the earthy matter being 
secreted within the outer wall and between each pair of 
partitions. So that a corallite is a short tube with vertical 
septa radiating towards the centre. 132 A sclerobasic Coral 
is a true exoskeleton, and is distinguished by being smooth 
and solid. The Polyps, having eight fringed tentacles, are 
situated on the outside of this as a common axis, and are con¬ 
nected together by the fleshy ccenosarc covering the Coral. 

(1) Sclerodermic Corals.— Astrcea is a hemispherical mass 
covered with large cells. Meandrina , or “ Brain-coral,” 
is also globular; but the mouths of the Polyps open into 
each other, forming furrows. Fungia , or “ Mushroom- 
coral,” is disk-shaped, and differs from other kinds in be¬ 
ing the secretion of a single gigantic Polyp, and in not 
being fixed. Madrepora is neatly branched, with pointed 
extremities, each ending in a small cell about a line in 
diameter. Forties, or “ Sponge-coral,” is also branching, 
but the ends are blunt, and the surface comparatively 
smooth. Tubipora, or “ Organ -pipe coral,” consists of 
smooth red tubes connected at intervals by cross-plates. 
The Astrcea, Meandrina, Madrepora, and Forties are the 
chief reef-forming Corals. They will not live in waters 


CCELENTERATA. 


253 




Fw. 201.—.3 tadrepora axpera, living and expanded; natural size. Pacific. 

whose mean temperature in the coldest month is below 
68° Fahr., nor at greater depth than twenty fathoms. The 
most luxuriant reefs are in the Central and Western Pa¬ 
cific and around the West Indies. 


Fig. 202 .—Ctenactis echinata , or “ Mushroom-coralone fourth natural size. Pacific. 







254 


COMPARATIVE ZOOLOGY. 



Fig. 203.— Astrceapallida; natural size. Fejee Islands. 


A coral-reef is formed by many Corals growing togeth¬ 
er. It is to the single Coral-stock as a forest is to a tree. 



Fig. 204.— Diploria eerebnformiSy or “Brain-coralone half natural size. Bermudas. 












CCELENTERATA, 


255 



Fig. 20&.—Astrcea rotulosa. West Indies. 


The main kinds of reefs are fringing, where the reef is 
close to the shore; barrier , where there is a channel be- 



Fig. 206.—Cell of Madrepore Coral, 
magnified. The cup-like depres¬ 
sion at. the top of a coral skeleton 
is called calicle. 



Fig. 207.—Fragment of Red Coral ( Coral- 
Hum, rubrum), showing living cortex 
and expanded Polyps. Mediterranean. 


256 


COMPARATIVE ZOOLOGY. 


tween reef and shore; encircling , where there is a small 
island inside of a large reef; and coral islands , or atolls , 
where there is simply a reef with no land inside of it. All 
reefs begin as fringing-reefs, and are gradually changed 
into the other forms by the slow sinking of the bottom of 
the ocean. This sinking must be slower than the upward 
growth of the reef, else it will be drowned out. Probably 
the reef does not grow more than five feet in a thousand 
years; and, as reefs are often more than two thousand 
feet thick, they must be very old. 

(2) Sclerobasic Corals.— Cor allium rubrum , the precious 
coral of commerce, is shrub-like, about a foot high, solid 
throughout, taking a high polish, finely grooved on the 
surface, and of a crimson or rose-red color. In the living 

J O 



Fig. 208.— Sea-fan (Gorgonia) and Sea-pen ( Pennatula ). 


state the branches are covered with a red coenosarc stud¬ 
ded with Polyps. Gorgonia , or “ Sea-fan,” differs from 
all the other representative forms in having a horny axis 
covered with calcareous spicules. The branches arise in 
the same vertical plane, and unite into a beautiful net¬ 
work. 






ECHINODERMATA. 


257 


CLASS III.—Ctenophora. 

The Ctenophora (as the Pleuro- 
brachia , Cestum, and Beroe) secrete 
no hard deposit. They are trans¬ 
parent and gelatinous, swimming on 
the ocean by means of eight comb¬ 
like, ciliated bands, which work like 
paddles. The body is not contrac¬ 
tile, as in the Jelly-fishes. They are 
considered the highest of Ccelente- 
rates, having a complex nutritive ap- Ft» 
paratus and a definite nervous sys- ptleu * ); 

tern. 



A Ctenophore ( Pleu- 
natural 


Subkingdom III. —Echinodermata. 


The Echinoderms, as Star-fishes and Sea-urchins, are 
distinguished by the possession of a distinct nervous sys¬ 
tem (a ring around the mouth); an alimentary canal, com- 



Fig. 210.—Forms of Echinoderms, from radiate to annnlose type: a, Crinoids; 6, 
Ophiurans; c, Star-fish; d, Echini; e, Holothurians. 

pletely shut off from the body-cavity, and having both 
oral and anal apertures; a water-vascular system of circu- 

17 








258 


COMPARATIVE ZOOLOGY. 


lar and radiating canals, connected with the outside water 
by means of the madreporic tubercle, and a symmetrical 
arrangement of all the parts of the body around a central 
axis in multiples of five. 133 There are four principal class¬ 
es, all exclusively marine and solitary, and all having the 
power of secreting more or less calcareous matter. 

Class I.— Crinoidea. 

The Crinoids, or “ Sea-lilies, 1 ” are fixed to the sea-bottom 
by means of a hollow, jointed, flexible stem. On the top 
of the stem is the body proper, resembling a bud or ex¬ 
panded flower, containing the digestive apparatus, with 
the surrounding arms, or tentacles. The mouth looks up¬ 
ward. There is a complete skeleton for strength and sup¬ 
port, the entire animal—body, arms, and stem—consisting 
of thousands of stellate pieces connected together by liv¬ 
ing matter. Crinoids were very abundant in the old geo- 
ologic seas, and many limestone strata were formed out of 
their remains. They are now nearly extinct: dredging 
in the deep parts of the oceans has brought to light a few 
living representatives. 

Class II. —Asteroidea. 

Ordinary Star-fishes consist of a flat central disk, with 
five or more arms, or lobes, radiating from it, and con¬ 
taining branches of the viscera. The skeleton is leathery, 
hardened by small calcareous plates (twelve thousand by 
calculation), but somewhat flexible. The mouth is below; 
and the rays are furrowed underneath, and pierced with 
numerous holes, through which pass the sucker-like tenta¬ 
cles—the organs of locomotion and prehension. The red 
spots at the ends of the rays are eyes. The usual color of 
Star-fishes is yellow, orange, or red. They abound on ev¬ 
ery shore, and are often seen at low tide half buried in 
the sand, or slowly gliding over the rocks. Cold fresh 





ECHINODERMATA. 


259 



211.—A living Crinoid (Pentacrinun asteria ); one fourth natural size. 

Indian Seas. 


West 









260 COMPARATIVE ZOOLOGY. 

water is instant death to them. They have the power of 
reproducing lost parts to a high degree. They are very 
voracious, and are the worst enemies of the Oyster. 


Fig. 212.—Under-surface of Star-fish (Gronicuster reticulatus ), showing ambulncral 
grooves and protruded suckers. 

About one hundred and fifty species are known. These 
may be divided into three groups: (1) species having four 
rows of feet, represented by the common five-fingered 
Asterias ; (2) species having two rows of feet, as the many- 
rayed Solaster, or “ Sun-star,” and the pentagonal Goni- 
aster; (3) species having long, slender arms, which are not 
prolongations of the body, and are not provided with suck¬ 
ers, as the Ophiura , or “ Brittle-star,” and Astrophyton, or 
“ Basket-fish.” The last are of inferior rank, and resemble 




ECHINODERMATA. 


261 

inverted, stemless Crinoids. The digestive sac is confined 
to the disk, and the madreporic tubercle is concealed. 



Fig. 213. - Ophiocoma Riissei , an Ophiuran; natural size. West Indies. 


Class III. —Echinoidea. 

The Sea-urchin is encased in a thin, hollow shell cov¬ 
ered with spines, and varying in shape from a sphere to a 
disk. 184 The mouth is underneath, and contains a dental 
apparatus more complicated than that of any other creat¬ 
ure. It leads to a digestive tube, which extends spirally 
to the summit of the body. The spines are for burrow¬ 
ing and locomotion, and are moved by small muscles, each 
being articulated by ball-and-socket joint to a distinct tu¬ 
bercle. When stripped of its spines, the shell (or “test”) 
is seen to be formed of a multitude of pentagonal plates, 
fitted together like a mosaic. 135 Five double rows of plates, 


262 


COMPARATIVE ZOOLOGY. 



passing from pole to pole, like the ribs of a melon, alter¬ 
nate with five other double rows. In one set, called the 

ambulacra , the 
plates are perfo¬ 
rated for the pro¬ 
trusion of tubular 
feet, or suckers, as 
in the Star-fish. 
So that altogether 
there are twenty 
series of plates— 
ten ambulacral, 
andteninterambu- 
lacral. The shell 
is not cast, but 
grows by the en- 

Fig. 214. -Under-surface of a Sea-urchin (Echinus escu - ~ 

lentus), showing rows of suckers among the spines, lai’gement ot each 

Bti,lshsea8 - individual plate, 

and the addition of new ones around the mouth and the 
opposite pole. Every part of an Echinus, even sections 
of the spines, show the principle of radiation. If the up¬ 
per surface of a Star-fish should shrink so as to bring 
the points of the arms to meet above the mouth, we 
should have a close imitation of a Sea-urchin. Echini live 
near the shore, in rocky holes or under sea-weed. They 
are less active than Star-fishes; but, like them, feed on 
Mollusks and Crabs. They reproduce by minute red eggs. 

Regular Echini, as the common Cidaris , are nearly 
globular, and the oral and anal openings are opposite. 
Irregular Echini, as the Clypeaster , are flat, and the anal 
orifice is near the margin. 


Class IV.— Holothuroidea. 

These worm-like “ Sea-slugs,” as they are called, have a 
soft, elongated body, with a tough, contractile skin contain- 



ECHINODERMATA.—VERMES. 


2 63 


ing calcareous granules. One end, the head, is abruptly 
terminated, and has a simple aperture for a mouth, en¬ 
circled with feathery tentacles. There are usually five I 
longitudinal rows of ambulacral suckers, but only three 
are used for locomotion, of which one is more developed 
than the rest. The mouth opens into a pharynx leading 
to a long intestinal canal. Holothurians have the singular 
power of ejecting most of their internal organs, surviving 



Fig. 215.—Sea-slugs (Holothuria). 


for some time the loss of these essential parts, and after¬ 
wards reproducing them. They occur on nearly every 
coast, especially in tropical waters, where they sometimes 
attain the length of three or four feet. As found on the 
beach after a storm, or when the tide is out, they are 
leathery lumps, of a reddish, brownish, or yellowish color. 
They may be likened to a Sea-urchin devoid of a shell, 
and long drawn out, with the axis horizontal, instead of 
vertical. 

Snbkingdom IV. —Vermes. 

The Vermes, 138 or Worms, form the lowest subkingdom 
of the bilaterally symmetrical animals. The group in¬ 
cludes animals very different in form and rank, and the 
different classes are widely separated from each other. 






2G4 


COMPARATIVE ZOOLOGY. 


It has also close relations with the other subkingdoms of 
the bilaterally symmetrical animals. Through the Poly- 
i zoa and Brachiopoda, it approaches the Mollusca; through 
the Annelides, the Arthropoda; and through other forms, 
the Tunicata, and so the Vertebrata. The subkingdom 
thus stands in the centre of several subkingdoms, with 
affinities towards all. Nor are indications of connection 
with Coelenterata and Echinodermata wanting. 

The Yermes are bilaterally symmetrical animals,with one 
or many segments, no jointed legs. They usually have a soft 
skin, and peculiar excretory organs—the segmental organs. 

Many of the Worms are parasitic, and most of the En- 
doparasites belong to this group. 

There are numerous classes, of which only the most im¬ 
portant are mentioned. 

Class I.— Platyhelminthes. 

The Flat - worms 
include some free 
forms, as the Plana- 
ria, common in fresh 
water, and the 
worms and Flukes 
among the parasites. 

The Tape-worm 
consists of the so- 
called head—the 
proper worm — and 
the body segments, 

I 

Fig. 216—Tape-worm {Taenia solium) : a, head; &,e, Fig. 21T _Plauarian 

d, segments of the body. worm. 







VERMES. 


265 


which are really reproductive joints. It develops from 
the egg in the digestive canal of the Pig, burrows into 
the cellular tissue of the animal, and there becomes en¬ 
cased. It thus causes the disease “ measles.” If the pork 
be eaten by man, in an uncooked condition, this case is 
dissolved by the gastric juice, and the embryo develops 
into the Tape-worm, attaching itself to the intestine by 
its “head,” and budding off the reproductive segments. 
As these become ripe and filled with fertilized eggs, they 
are detached, and pass off with the excrement. 

The disease called “ rot,” in Sheep, is produced by the 
Fluke (Disto?na), a member of this class. 

Class II.— Nematelminthes. 

The Round, or Thread, Worms include free forms, as 
the Yinegar-eel; parasitic forms, as the Pin-worm and 
Trichina; and forms 
free when adult, and 
parasitic when young, 
as the Hair-worm ( Gor¬ 
dius ). 

The Trichina is usu¬ 
ally derived by Man 
from the flesh of the 
Pig. It exists in the 
muscles, enclosed in mi¬ 
croscopic cases. If the 
meat be eaten uncooked 
or partially cooked, the 
cases are dissolved, and 
the Trichinae become 
sexually mature in the 
intestines. The young 

are produced and bur- Fio. 21S.— Trichina spiralis: I, male; a, mouth; 

* . c, intestine; II, capsules, with Trichin® in mus* 

TOW their way into the cle, much enlarged. 



COMPARATIVE ZOOLOGY. 


266 

muscles, where they become encysted. In burrowing, they 
cause great pain and fever, and sometimes death. The 
adult Worm is about ^ inch long. 

Class III.— Rotifera. 

The Wheel-animalcules, mostly found in fresh water, 
are minute Worms of few segments, having on the ante¬ 
rior end a disk ciliated on the edge, 
whence their name. They are from 
roi 7 to A of an inch long. They can 
bear drying and revivifying, like seeds. 

Class IY.— Polyzoa. 

These minute Worms resemble the 
Polyps in appearance, living in clusters, 
each individual inhabiting a delicate 
cell, or tube, and having a simple mouth 
surrounded with ciliated tentacles. The 
colony often takes a plant - like form; 
sometimes spreads, like fairy-chains or 
lace-work, over other bodies; or covers 
rocks and sea-weeds in patches with a 
delicate film. The majority secrete car- 
Fig. 219 . — Rotifer, or bonate of lime. A Polyzoan shows its su- 
( Hydaton ]™Wghiy periority to the Coral, which it imitates, 
magnified. j n possessing a distinct alimentary canal 

and a w T ell-defined nervous system. The cells of a group 
never have connection with a common tube, as in Ccelen- 
terates. There are both marine and fresh-water species. 

This group and the next following are related to the 
Mollusca. 

Class Y.— Brachiopoda. 

These Worms have a bivalve shell, the valves being 
applied to the dorsal and ventral sides of the body. The 
valves are unequal, the ventral being usually larger, and 






VERMES. 


267 



Fig. 220.—Polyzoans: 1. Hornera lichenoides, natural size. 2. Branch of the same, 
magnified. 3. Discopora Skenei , greatly enlarged. 


more convex; but they are symmetrical, i. e ., a vertical 
line let fall from the hinge divides the shell into two 
equal parts. The ventral valve has, in the great major¬ 
ity, a prominent beak, perforated by a foramen, or hole, 
tlirough which a fleshy foot protrudes to attach the ani¬ 
mal to submarine rocks. The valves are opened and shut 


by means of muscles, and in 
most cases they are hinged, 
having teeth and sockets 



Fig. 221.— A Bracuiopod (Terebratulina 
septentrionali*). Atlantic coast. 

near the beak. The mouth 
faces the middle of the mar¬ 
gin opposite the beak; and 
on either side of it is a long, 



Fig. 222.—Dorsal Valve of a Brachiopod 
(Terebratula), showing, in descending 
order, cardinal process, dental sockets, 
hinge-plate, septum, and loop support¬ 
ing the ciliated arms. 














268 


COMPARATIVE ZOOLOGY. 


fringed “arm,” generally coiled up, and supported by a 
calcareous framework. The animal, having no gills, re¬ 
spires by the arms and the mantle. Brachiopods were 
once very abundant, over two thousand extinct species 
having been described; but less than a hundred species 
are now living. 137 They are all marine, and fixed; but of 
all Worms, they enjoy the greatest range of climate and 
depth. 

Class VI.—Annelides. 

The Annelides include the highest and most specialized 
Worms. They have many segments, spines or suckers 
for locomotion, a superoesophageal brain, a ventral chain 



Fio. 223.—Marine Worm (Cirratulus grandis), with extended cirri. Atlautic. 


of ganglia, and a closed blood-system. There are three 
main divisions: the flattened Leeches, without definite 
segments or bristles, and with suckers for locomotion ; the 




MOLLUSCA. 


2G9 


Earth-worms and their allies, which have few bristles on 
each segment (Oligochcetoe ); and the Sea-worms, with nu¬ 
merous bristles, arranged in two clusters on each side of 
each segment ( Polychcetce ). 

These last are the largest of the Worms, and may have 
a distinct head, bearing tentacles and eyes. The oesopha¬ 
gus is often turned in, so as to form a proboscis, which 
bears horny jaws, and can be protruded at the will of the 
animal (Fig. 17). 

Snbkingdom V. —Mollusca. 

A Mollusk is a soft-bodied animal, without internal 
skeleton, and without joints, covered with a moist, sensi¬ 
tive, contractile skin, which, like a mantle, loosely envel¬ 
ops the creature. In some cases the skin is naked, but 
generally it is protected by a calcareous covering (shell). 
The length of the body is less in proportion to its bulk 
than in other animals. The lower class has no distinct 
head. The nervous system consists of three well-devel¬ 
oped pairs of ganglia, which are principally concentrated 
around the entrance to the alimentary canal, forming a 
ring around the throat. The other ganglia are, in most 
cases, scattered irregularly through the body, and in such 
the body is unsymmetrical. The digestive system is 
greatly developed, especially the liver, as in most aquatic 
animals. Except in the Cephalopods, the muscles are at¬ 
tached to the skin, or shell. There is a heart of two 
chambers (auricle and ventricle) or three (two auricles 
and ventricle). As in all Invertebrates, the heart is arte¬ 
rial. In Mollusks, with rare exceptions, we find no repe¬ 
tition of parts along the antero-posterior axis. They are 
best regarded as Worms of few segments, which are fused 
together and much developed. The total number of 
living species probably exceeds twenty thousand. The 
great majority are water-breathers, and marine; some are 


270 


COMPARATIVE ZOOLOGY. 



fluviatile or lacustrine, and a few are terrestrial air-breath¬ 
ers. All bivalves, and nearly all univalves, are aquatic. 
Each zone of depth in the sea has its particular species. 

Class I. —Lamellibranchiata. 

Latnellibranchs are all ordinary bivalves, as the Oyster 
and Clam. The shells differ from those of Brachiopods 
in being placed on the right tind left 
sides of the body, so that the hinge is on 
the back of the animal, and in being 
unequilateral and equivalved. 138 The 
umbo, or beak, is the point from which 
the growth of the valve commences. 
Fig. 224.—Pearl oyster Both Brachiopods and Lamellibranchs 
are headless; but in the latter the mouth 
urai size. Ceylon. p 0 i n ts the same way as the umbo, i. e ., 
towards the anterior part. The length of the shell is 
measured from its anterior to its posterior margin, and its 
breadth from the dorsal side, where the 
hinge is, to the opposite, or ventral, edge. 

The valves are united to the animal by 
one muscle (as in the Oyster), or two (as 
in the Clam), and to each other by a 
hinge. In some species, as some fresh¬ 
water Mussels, the hinge is simply an 
elastic ligament, passing on the outside 
from one valve to the other just behind 
the beak, so that it is on the stretch when 
the valves are closed, and another placed Fi«- 225. — salt -water 
between the edges of the valves, so that AtLm/c 

it is squeezed as they shut, like the spring coa8t8 ‘ 
in a watch-case. Such bivalves are said to be edentulous. 
But in the majority, as the Clam, the valves also articulate 
by interlocking parts called teeth. The valves are, there¬ 
fore, opened by the ligaments, and closed by the muscles. 



MOLLUSCA. 271 

The margin of the shell on which the ligament and teeth 
are situated is termed the hinge-line. 

Lamellibranchs breathe by four plate-like gills (whence 
the name), two on each side underneath the mantle (Fig. 
78). In the higher forms, the mantle is rolled up into 
two tubes, or siphons, for the inhalation and exhalation of 
water. They feed on infusorial particles filtered from the 
water. A few are fixed; the Oyster, e. g ., habitually lying 



Fig. 226—Lamellibranch ( Mactra ): a, foot; b, c, siphons. 


on its left valve, and the Salt-water Mussel hanging to 
the rocks by a cord of threads called “ byssus;” but most 
have a “foot,” by which they creep about. Unlike the 
Oyster, also, the majority live in an erect position, rest¬ 
ing on the edges of their shells. Over four thousand 
living species are known. These are fresh-water and 
marine, and range from the shore to a depth of a thou¬ 
sand feet. 

The chief characters for distinguishing Lamellibranchs 
are the muscular impressions, 139 whether one or two; the 
presence of a pallial sinus, which indicates the possession 
of siphons; the structure of the hinge, and the symmetry 
of the valves. 

The following are the leading types of structure, as 
shown by the shells: 

1. Monomya: with one adductor muscle; no siphons; 
foot wanting, or very small; shell unequivalve and eden- 


272 


COMPARATIVE ZOOLOGY. 


tulous—as the Oyster ( Ostrea ), Scallop (. Pecten ), and Pearl 
Oyster (Avicula). 

2. Heteromya: with two unequal adductor muscles and 
no siphons—as the Sea-mussel {My- 
tilus). 

3. Isomya: with two equal ad¬ 
ductor muscles. There are two sec¬ 
tions of this order: a. Those with 
no siphons, and hence no pallial 
sinus — as the Fresh-water Mussel 
( TJnio), Cockle ( Oardium ), and “ the 
F 2Z?TJTrfZZ gi“"t of the bivalve race” {Tridac- 
size. China seas. J. Those with siphons and pal¬ 

lial sinus—as the common Clam {Mya), Quohog ( Venus), 
and Kazor-shell {Solen)A* 



Class II.— Gasteropoda. 

The Snails are, with rare exceptions, all univalves. 141 
The body is coiled up in a conical shell, which is usually 



Fio. 228.—Whelk ( Buccinum ), showing operculum, o, and siphon, «. 


spiral, the whorls passing obliquely (and generally from 
right to left), 143 around a central axis, or “columella.” 






mollusca. 


273 

When the columella is hollow (perforated), the end is 
called the “ umbilicus.” When the whorls are coiled 
around the axis in the same plane, we have a diseoidal 
shell, as the Planorbis. The mouth, or “aperture,” of 
the shell is “entire” in most vegetable-feeding Snails, and 
notched or produced into a canal for the siphons in the 
carnivorous species. The former are generally land and 
fresh-water forms, and the latter all marine. In some 
Gasteropods, as the River-snails and most Sea-snails, a 
horny or calcareous plate ( operculum) is secreted on the 
foot, which closes the aperture when the animal with¬ 
draws into its shell. In locomotion, the shell is carried 
with the apex directed backward. 

The body of most Gasteropods is unsymmetrical, the 
organs not being in pairs, but single, and on one side, 
instead of central. The mantle is continuous around the 
body, not bilobed, as in Lamellibranchs. A few, as the 
common Garden-snail, have a lung; but the vast majority 
breathe by gills. The head is more or less distinct, and 
provided with two tentacles, with auditory sacs at their 
bases; two eyes, which are often on stalks; and a strap¬ 
like tongue covered with minute teeth. The heart is sit¬ 
uated, in the majority, on the right side of the back, and 
has two cavities. The nervous ganglia are united into an 
oesophageal ring or collar. All, except the Pteropods, 
move by means of a ventral disk or foot. 

Gasteropods are now the reigning Mollusks, comprising 
three fourths of all the living species, and are the types 
of the subkingdorn. They have an extraordinary range 
in latitude, altitude, and depth. 

Omitting a few rare and aberrant forms, we may sepa¬ 
rate the class into the following orders: 

1. Pteropods .—These are small, marine, floatings Mol- 
lusks, whose main organs of motion resemble a pair of 
wings or fins coming out of the neck, whence the com- 

18 


274 


COMPARATIVE ZOOLOGY. 


inon 


name, “ Sea - butterflies.” Many have a delicate, 


transparent shell. 


The head has six appendages, armed 
with several hundred thousand micro¬ 
scopic suckers—a prehensile apparatus 
unequalled in complication. Pteropods 
occur in every latitude, but generally 
in mid-ocean, and in the arctic regions 
are the food of Whales and Sea-birds. 
2. Opisthobranohs .—These low Gas- 
aka tridentata). Atlantic, teropods are, for the most part, naked 
Sea-slugs, a few only having a small shell. The feathery 
gills are behind the heart (whence the name). They are 
found in all seas, from the arctic to the torrid, generally 
on rocky coasts. When disturbed, 
most of them draw themselves up 
into a lump of jelly or tough skin. 



Fig 


—A Pteropod {Hrj- 




Fig. 230.—A Tritouian (Dendronolus arboreacens). 
British seas. 


Fig. 231 _ Butla mnpni- 

la, or “Bubble-shell ; n 
three fourths natural 
size. Indian Ocean 


Examples: Sea-lemon (Doris), the beautiful Tritonia, the 
painted yEolis, the Sea-hare ( Aplysia •), which discharges 
a purple fluid, and the Bubble-shell (Bulla). 

3. Pulmonates .—These air-breathing Gasteropods, rep¬ 
resented by the familiar Snail, have the simplest form of 
lung—a cavity lined with a delicate net-work of blood¬ 
vessels, which opens externally on the right side of the 
neck. This is the mantle-cavity. The entrance is closed 
by a valve, to shut out the water in the aquatic tribes, 
and the hot, dry air of summer days in the land species. 
They are all fond of moisture, and are more or less slimy. 
Their shells are lighter (being thinner, and containing less 




MOLLUSCA. 


275 

earthy matter) than those of marine Mollusks, having to 
be carried on the back without the support of the water. 




Fig. 232 — A, Laud-snail {Helix); B, C, D, Slugs ( Umax )• E, F, (?, Poud-snails 
(Limnce a, Paludina, and Planorlm). 

Their eggs are laid singly, while the eggs of other orders 
are laid in chains. 

They are found in all zones, but are 
most numerous where lime and moisture 
abound. All feed on vegetable matter. 

A few are naked, as the Slug; some are 
terrestrial; others live in fresh water. 

The Land - snails, represented by the 
common Helix , the gigantic Bulimue , 
and the Slug {Limax), are distinguished 
by their four “horns,” the short front 
pair being the true tentacles, and the 
long hinder pair being the eye-stumps. 

They have a saw-like upper jaw for 8ize - Guiana * 
biting leaves, and a short tongue covered with minute 
teeth. The Pond-snails, as Limnaea and Planorbis , differ 




276 


COMPARATIVE ZOOLOGY, 



ft 



D 


Fig. 230*. — Spindle- 
shell ( Fusus colus); 
one half natural 
size. Ceylon. 



Fig. 237. — Cassis rufa , or 
“Helmet-shell;” one fourth 
natural size. Indian Ocean. 



Fig. 23S.—Auger-shell 
(Terebra maculata ): 
one half natural 
size. China seas. 



Fio 239.—Cone-shell ( Conus 
marmoreus ); two thirds 
natural size. China seas. 



Fig. 240. —Chiton squa- 
r'losus ; one half natu¬ 
ral size. West Indies. 



Fig. 241. —Volute ( Voluta 
musica); one half nat¬ 
ural size. West Indies. 

























MOLLUSCA 


277 



Fig. 242. —Top-shell ( Turbo marmo- 
ratUH ); one fourth natural size. 
China seas. 



Fig. 243— Strombus gigas, or “Winged- 
shellone fifth natural size. West 
Indies. 


Fig. 244. 



— Paludina, a Fresh-water 
Snail. 



Fig. 245.—Key-hole Limpet (Fiasurella 
listeri). West Indies. 



Fig. 246 .—Ear-shell (II. tuberculata), and Dog-whelk (Xassa reticulata). England. 


































278 


.COMPARATIVE ZOOLOGY. 


in having no eye-stalks, the eyes being at the base of the 
tentacles. They are obliged to come frequently to the 
surface of the water to breathe. 

4. Prosobranchs. — These are aquatic Gasteropods, 
breathing by gills situated in front of the heart. They 
are the most highly organized and the most abundant of 
the crawling Mollusks. Nearly all are marine, and all 
have a shell. 

Among the lower forms are the singular Chiton , cov¬ 
ered with eight shelly plates; Limpet (Patella), well 
known to every sea-side visitor; and the beautiful Ear- 
shell (Haliotis), frequently used for ornaments and inlaid- 
work. 

In the higher Prosobranchs, the gills are comb-shaped 
and the sexes are distinct. The group includes all the 
spiral univalve sea-shells, and a few fresh-water shells. 
Many have the aperture entire, which is closed with an 
operculum: as the dull-colored Paludina and Melania 
from fresh water, and the pyramidal Trochus , pearly Tur¬ 
bo , screw-like Turritella, common Periwinkle ( Littorina ), 
and globular Natica from the sea. Others, the highest 
of the race, have the margin of the aperture notched or 
produced into a canal, and- are carnivorous and marine: 
such are nearly all the sea-shells remarkable for their 
beautiful forms, enamelled surfaces, and brilliant tints, as 
the Cowry ( Cyproea), Volute, Olive, Cone, Harp, Whelk 
(Buccinum), Cameo-shell (Cassis), Pock-shell (Murex), 
Trumpet-shell (Triton), Spindle-shell (Fusus), and Wing- 
shell (>Strombus). 


Class III. —Cephalopoda. 

The Cephalopods stand at the head of the subkingdom. 
The head is set off from the body by a slight constriction, 
and furnished with a pair of large, staring eyes, a mouth 
armed with a rasping tongue and a parrot-like beak, and 


MOLLUSC A. 279 

eight or more tentacles or arms. The body is symmetri¬ 
cal, and wrapped in a muscular mantle. 

The nervous system is more concentrated than in other 
Invertebrates; the cerebral ganglia are partly enclosed in 
a cartilaginous cranium. All the five senses are present. 
The class is entirely marine (breathing by plume-like gills 
on the sides of the body), and carnivorous. The naked 
species are found in every sea. Those with chambered 
shells (as Nautilus , Ammonites , and Qrthoceras ) were once 
very abundant: more than two thousand fossil species are 
known, blit only one living representative — the Pearly 
Nautilus. 

1. Tetrabranclis . — This order is characterized by the 
possession of four gills, forty or more short tentacles, and 
an external, chambered shell. The partitions, or septa, of 
the shell are united by a tube called “ siphuncle,” and the 



Fig. 247. —Pearly Nautilus, witu shell bisected ; one half natural size. Indian Oceau. 

animal lives in the last and largest chamber. 143 The liv¬ 
ing Nautilus has a smooth, pearly shell, a head retractile 
within the mantle or “hood,” and calcareous mandibles, 
well fitted for masticating Crabs, on which it feeds. This 





280 COMPARATIVE ZOOLOGY. 

straggler of a mighty race dwells in the deep parts of the 
Indian Ocean, crawling on the bottom ; and, while the 
shell is well known, only a few specimens of the animal 
have ever been obtained. 

2. Dibranchs .—These are the most active of Mollnsks, 
and the tyrants of the lower tribes. Among them are 
the largest of invertebrate animals. They are naked, hav¬ 
ing no external shell covering the body, but usually a 
horny or calcareous part within. They have a distinct 

head, prominent eyes, horny 
mandibles, eight or ten arms 
furnished with suckers, two 
gills, a complete tubular fun¬ 
nel, and an ink-bag contain¬ 
ing a peculiar fluid (sepia), of 
intense blackness, with which 
the water is darkened to fa¬ 
cilitate escape. They have 
the power of changing color, 
like the Chameleon. They 
crawl with their arms on 
the bottom of the sea, head 
downward, and also swim 
backward or forward, usual¬ 
ly with the back downward, 
by means of fins, or squirt 
themselves backward by forc¬ 
ing water forward through 
their breathing funnels. 

The Paper Nautilus ( Ar - 
gonauta) and the Poulpe ( Octopus ) have eight arms. The 
female Argonaut secretes a thin, unchambered shell for 
carrying its eggs. The Squid (Loligo) and Cuttle-fish 
(Sepia) have ten arms, the additional pair being much 
longer than the others. Their eyes are movable, while 



Fig. 248. — Cuttle-fish {Sepia officinalis)- 
one fifth uatural size. Atlantic coasts. 



ARTHROPODA. 


281 


those of the Argonaut and Poulpe are fixed. The Squid, 
so much used for bait by cod-fishermen, has an internal 
horny “pen,” and the Cuttle has a spongy, calcareous 
“ bone.” The extinct Belemnite had a similar structure. 



Fio. 249.—Paper Nautilus (Argonauta argo ): 1, swimming towards a by ejecting wa¬ 
ter from funnel, b; 2, crawling on the bottom; 3, coiled within its shell, which is 
oue fourth natural size. Mediterranean. 


Squid have been found with a body seven feet and arms 
twenty-four feet long, and parts of others still larger—as 
much as fifty feet in total length. 


Subkingdom VI.—Arthropoda. 


This is larger than all the other subkingdoms put to¬ 
gether, as it includes the animals witli jointed legs, such 
as Crabs and Insects. These differ widely from the Mol- 
luscan type in having numerous segments, and in show¬ 
ing a repetition of similar parts; and from the Worms 
in having a definite number of segments and jointed 

legs- 

The skeleton is outside, and consists of articulated seg¬ 
ments or rings. The limbs, when present, are likewise 
jointed and hollow. The jaws move from side to side. 
The nervous system consists mainly of a double chain of 



2S2 


COMPARATIVE ZOOLOGY. 


ganglia running along the ventral surface of the body 
under the alimentary canal. The brain is in the form of 
a ring encircling the gullet. The alimentary canal and 
the circulatory apparatus are nearly straight tubes lying 
lengthwise — the one through the centre, and the other 
along the back. The skeleton is composed of a horny 
substance (chitine), or of this substance with carbonate of 
lime. All the muscles are striated. 

There are four classes, of which the first is water-breath¬ 
ing, and the others air-breathing. 

Class I.— Crustacea. 

The Crustacea 144 are water-breathing Arthropoda, usu¬ 
ally with two pairs of antennae. 145 Among them are the 
largest, strongest, and most voracious of the subkingdom, 
armed with powerful claws and a hard cuirass bristling 
with spines. Although constructed on a common type, 
Crustaceans exhibit a wonderful diversity of external 
form: contrast, for example, a Barnacle and a Crab. We 
will select the Lobster as illustrative of the entire group. 

A typical Crustacean consists of twenty-one segments, 
of which seven belong to the head, seven to the thorax, 
and seven to the abdomen. 140 In the Lobster, however, 
as in all the higher forms, the joints of the head and tho¬ 
rax are welded together into a single crust, called the 
cejohalo-thorax. On the front of this shield is a pointed 
process, or rostrum; and attached to the last joint of the 
abdomen (the so-called “tail”) is the sole representative 
of a tail—the telson. This skeleton is a mixture of chitine 
and calcareous matter. 147 

On the under-side of the body we find numerous ap¬ 
pendages, feelers, jaws, claws, and legs beneath the cepli- 
alo-thorax, and flat swimmerets under the abdomen. In 
fact, as a rule, every segment carries a pair of movable 
appendages. The seven segments of the head are com- 


ARTHROPOD A. 


283 



pressed into a very small space, yet have the following 
members: the eye-stalks; the short and the long anten¬ 
nas; the mandibles, or jaws, between which the mouth 
opens; the tw r o pairs of maxillge; and a pair of modified 
limbs, called 66 foot-jaws.” The thorax carries two more 
pairs of foot-jaws and five pairs of legs. The foremost 
legs, “ the great claws,” 
are extraordinarily de¬ 
veloped, and terminat¬ 
ed by strong pincers 
(< ckelce ). Of the four 

slender pairs succeed¬ 
ing, two are furnished 
with claws, and two 
are pointed. The last 
pair of swimmerets, to¬ 
gether with the telson, 
form the caudal fin— 
the main instrument of 
locomotion; the others 
(called “false feet”) 
are used by the female 
for carrying her eggs. 

The eyes are raised on 
stalks so as to be mov¬ 
able (since the head is 

and are compound, 
made up of about two 
thousand five hundred square facets. At the base of each 
small antenna is a minute sac, whose mouth is guarded by 
hairs: this is the organ of hearing. The gills, twenty on 
a side, are situated at the bases of the legs and enclosed in 
two chambers, into which water is freely admitted, in fact, 
drawn, by means of a curious attachment to one of the 


fixed to the thorax), 


Fig. 250. —Under-side of the Cray-fish, or Fresh¬ 
water Lobster (Astacus Jluviatilis): a, first pair 
of antennae; b, second pair; c, eyes ; d, open¬ 
ing of kidney; e, foot-jaws ; /, g , first and fifth 
pair of thoracic legs; h , abdominal feet; f, 
aims; k, caudal fin. 








284 


COMPARATIVE ZOOLOGY. 


maxillse, which works like the “screw” of a propeller. 
The heart is a single oval cavity, and drives arterial blood 
—a dusky fluid full of corpuscles. The alimentary canal 
consists of a short gullet, a gizzard-like stomach, and a 
straight intestine. 

Crustaceans pass through a series of strange metamor' 
phoses before reaching their adult form. They also peri¬ 
odically cast the shell, or moult, every part of the integu¬ 
ment being renewed; and another remarkable endowment 
is the spontaneous rejection of limbs and their complete 
restoration. Many species are 
found in fresh water, but the class 
is essentially marine and carnivo¬ 
rous. 

Of the numerous orders of this 
great class we will mention only 
four: 

1. Cirripeds , distinguished by 
being fixed, by having a shelly 
covering, and by their feathery 
arms {cirri). Such are Barnacles 
(Lepas) an d A cor n-shells ( Balarms), 
so common on rocks and timbers 
by the sea-shore. 

2. Bntomostracans , which agree 
in having a horny shell and no abdominal limbs; repre¬ 
sented by the little Water-fleas ( Cyclops ) of our ponds, and 



Fig. 252 — Amphithoe maculata: a Sand-flea. 


the Brine-shrimps ( Artemia ), and many others. The King- 
crabs (. Limulus ) and the extinct Trilobites were formerly 



tradecapod. U. S. coast. 















ARTHKOPODA. 


285 



Fig. 253.—Barnacles, or Pedunculate Cirripedes {Lepas anatifera). 


united to this class, but now are known to be widely re¬ 
moved from it. The former is by some authors removed 
from the Crustacea. 

3. Tetradecapods , small, fourteen-footed species; as the 



Fig. 254.—Acorn-shells ( Balamis ) on Fig. 255.—Water-fleas: 1 , Cyclops communis; 

the Shell of a Whelk ( Buccinum ). 2. Cypris unifasciata; 3, Daphnia pulcx. 














286 COMPARATIVE ZOOLOGY. 

Wood-louse, or Sow-bug (Oniscus), so common in damp 
places, the Slaters (Idotea ),and the Sand-fleas ( Gammarus ), 
seen by the sea-side. 

4. Decapods , having ten legs, as the Shrimp ( Crangon ), 


Fig. 256. —Lobster (Homarus vulgaris). 


Fig. 257—Svvimmiug Crab ( Platyonychus>. 









ARTHROPODA. 


28T 


Cray-fish (Astacus), Lobster (. Homarus ), and Crab ( Can - 
cer ). Crabs differ from Lobsters chiefly in being formed 
for creeping at the bottom of the sea instead of swim¬ 
ming, and in the reduction of the abdomen or “tail” to a 
rudiment, which folds into a groove under the enormous 
thorax. They are the highest and largest of living Crus¬ 
tacea: they have been found at Japan measuring fifteen 
feet between the tips of the claws. 


Class II.— Arachnida. 

The Arachnids are closely related to the Crustaceans, 
having the body divided into a cephalo-thorax and abdo¬ 
men. 148 To the former are attached eight legs of seven 
joints each; the latter has no locomotive appendages. 
The head carries two, six, or eight eyes, smooth and ses¬ 
sile (i. e ., not faceted and stalked, as in the Lobster), and 
approaching the eye of the Vertebrates in the complete¬ 
ness and perfection of their apparatus. The antennae, if 
present, are only two, and these are not “feelers,” but 
modified to serve for the prehension of food. 149 They are 
all air-breathers, having spiracles which open either into 
air-sacs or tracheae. The young of the higher forms un¬ 
dergo no metamorphosis after leaving the egg. 

Arachnids number nearly five thousand species. The 
typical forms are divided into three groups: 

1. Acarina , represented by the Mites and Ticks. They 
have an oval or rounded body, without any marked artic¬ 
ulations, the head, thorax, and 
abdomen being apparently 


merged into one. They have 

no brain \ only a single gan- 25 s. _^ Mite (Demodex /oWcuio- 

0-1 ion lodged in the abdomen, rum), one of the lowest Arachnids; 
& 1 & a parasite in humau hair-sacs; X 12o. 

They breathe by tracheae. The 

mouth is formed for suction, and they are generally para¬ 
sitic. The Mites ( Acarus ) are among the lowest of Ar- 



288 


COMPARATIVE ZOOLOGY. 


ticulates. The body is soft and minute. The Ticks 
( Ixodes ) have a leathery skin, and are sometimes half an 
inch long. The mouth is furnished with a beak for pierc¬ 
ing the animal it infests. 

2. Pedijpaljpi , or Scorpions, characterized by very large 
maxillary palpi ending in forceps, and a prolonged, joint¬ 
ed abdomen. The nervous and circulatory systems are 
more highly organized than those of Spiders; but the 
long, tail-like abdomen and the abnormal jaws place them 



Fig. 259.—Scorpion (under surface) and Centipede. 


in a lower rank. The abdomen consists of twelve seg¬ 
ments : the anterior half is as large as the thorax, with no 
well-marked division between; the other part is compara¬ 
tively slender, and ends in a hooked sting, which is perfo¬ 
rated by a tube leading to a poison-sac. The mandibles 
are transformed into small, nipping claws, and the eyes 
generally number six. Respiration is carried on by four 
pairs of pulmonary sacs which open on the under surface 





ARTHROPODA. 


289 


of the abdomen. The heart is a strong artery, extending 
along the middle of the back, and divided into eight separate 
chambers. Scorpions are confined tp the warm-temperate 
and tropical regions, usually lurking in dark, damp places. 

The Harvest-men ( Phalangium ), frequently seen about 
our houses, belong to this order. They have a short, thick 
body and extremely long legs, and breathe by tracheae. 

3. Araneina , or Spiders. They are distinguished by 
their soft, unjointed abdomen, separated from the thorax 
by a narrow constriction, and provided at the posterior 
end with two or three pairs of appendages, called “ spin- 



Fig. 260.—A, female Spider; B, male of same species; C, arrangement of the eyes. 


nerets,” which are homologous with legs. The office of 
the spinnerets is to reel out the silk from the silk-glands, 
the tip being perforated by a myriad of little tubes, 
through which the silk escapes in excessively fine threads. 
An ordinary thread, just visible to the naked eye, is the 

19 









290 


COMPARATIVE ZOOLOGY. 


union of a thousand or more of these delicate streams of 
silk. 150 These primary threads are drawn out and united 
by the hind legs. 

The mandibles are vertical, and end in a powerful hook, 
in the end of which opens a duct from a poison-gland in 
the head. The maxillae, or “ palpi,” which 
in Scorpions are changed to formidable claws, 
in Spiders resemble the thoracic feet, and are 
often mistaken for a fifth pair. The brain is 
of larger size, and the whole nervous system 
Fig. 261 .—spin- more concentrated than in the preceding or- 
der&!°?a?pai- der. There are generally eight simple eyes, 
piform organs. rare jy g j x> They breathe both by tracheae 
and lung-like sacs, from two to four in number, situated 
under the abdomen. All the species are carnivorous. 

The instincts of Spiders are of a high order. They are, 
perhaps, the most wily of Articulates. They display re¬ 
markable skill and industry in the construction of their 
webs; and some species (called “Mason Spiders”) even 
excavate a subterranean pit, line it with their silken tapes¬ 
try, and close the entrance with a lid which moves upon a 
hinge.’ 51 

Class III.— Myriapoda. 

Myriapods differ from Crustaceans and Spiders in hav¬ 
ing the thorax merged in the abdomen, while the head is 
free. In other words, the body is divided into similar 
segments, so that thorax and abdomen are scarcely distin¬ 
guishable. They resemble Worms in form and in the 
simplicity of their nervous and circulatory systems; but 
the skin is stiffened with chitine, and the legs (indefinite 
in number) are articulated. The legs resemble those of 
Insects, and the head appendages follow each other in the 
same order as in Insects—eyes, antennae, mandibles, max¬ 
illae, and labium. They breathe by tracheae, and have two 
antennae and a variable number of eyes. 



ARTHROPODA. 


291 


There are two orders: 

1. Chilognatha, having a cylindrical body, each segment 
furnished with two pairs of legs. They are of slow loco¬ 
motion, harmless, and vegetarian. The Thousand-legged 
Worm ( Julus ) is a common representative. 

2. Chilopoda , characterized by having a flattened body 
composed of about twenty segments, each carrying one 
pair of legs, of which the hindermost is converted into 
spines. They have longer antennae than the preceding, 
and the mouth is armed with two formidable fangs con¬ 
nected with poisonous glands. They are carnivorous and 
active. Such is the Centipede ( Scolopendra , Fig. 259). 

Class TV. —Insecta. 

Insects are distinguished by having head, thorax, and 
abdomen distinct, three pairs of jointed legs, one pair of 
antennae, and generally two pairs of wings. The number 
of segments in the body never exceeds twenty. The head, 
apparently one, is formed by the union of four segments. 
The thorax consists of three — the prothorax, mesothorax , 
and metathorax —each bearing a pair of legs; the wings, 
if present, are carried by the last two segments. The ab¬ 
domen is normally composed of ten segments, more or less 
movable upon one another. The skin is hardened with 
chitine, and to it, as in all Arthropods, the muscles are at¬ 
tached. The organs of sense are confined to the cephalic 
division of the body, the motor organs to the thoracic, and 
the vegetative to the abdominal. All the appendages are 
hollow. 

The antennae are inserted between or in front of the 
eyes. There is a great variety of forms, but all are tubu¬ 
lar and jointed. They are supposed to be organs of touch, 
and also seem to be sensitive to sound. The eyes are 
usually compound, composed of a large number of hexago¬ 
nal corneae, or facets (from fifty in the Ant to many thou- 


292 


COMPARATIVE ZOOLOGY. 


sands in the winged Insects). 






They are never placed on 
movable stalks, as the 
Lobster’s. Besides 
these, there are three 
simple eyes, called 
. ocelli . The mouth 

may be fitted for bit¬ 
ing ( masticatory ), as 
in Beetles, or for suck¬ 
ing ( suctorial ), as in 
Butterflies. The mas¬ 
ticatory type, which 
is the more complete, 
and ofwhich the other 
is but a modification, 
consists of four horny 
jaws (mandibles and 
maxillae) and an up¬ 
per and an under lip 
(labrum and labium). 
Sensitive palpi ( max¬ 
illary and labial) are 
developed from the 
lower jaw and lower 
lip. The labium is 
also prolonged into a 
ligula , or tongue. 

The legs are invari¬ 
ably six in the adult, 
the fore-legs direct¬ 
ed forward and the 
hinder pairs back¬ 
ward. Each consists 
of a hip, thigh, shank, 
and foot. 168 Some larvae have also “ false legs,” without 



Fig. 262.—Under surface of a Beetle (Harpalus cali- 
ginosu8): a, ligula; b, paraglossae; c, supports of 
labial palpi; d, labial palpus; e, mentum; /, in¬ 
ner lobe of maxilla; g, outer lobe; h, maxillary 
palpus; i, mandible; k, buccal opening; l , gula, 
or throat: m, buccal sutures; n, gular suture; o, 
prosternum; p , episternum of prothorax; p r , epi- 
meron; q , q\ q ", coxae; r, r, r, trochanters ; #, 
b s", femora, or thighs; t, t\ t", tibae; v, ventral 
abdominal segments; w, episternaof mesothorax; 

me 80 sternum; y , episterna of metathorax; y\ 
epimeron; z, metasternum. 















ARTHROPODA. 


293 


joints, on the abdomen, upon which they chiefly rely in 
locomotion. The wings are expansions of the crust, 
stretched over a net-work of horny tubes. The venation, 
or arrangement of these tubes (called veins and veinlets\ 
particularly in the fore-wings, is peculiar in each genus. 
In many Insects, the abdomen of the female ends in a 
tube which is the sheath of a sting, as in the Bee, or of an 
ovipositor , or “ borer,” as in the Ichneumon, by means of 
which the eggs are deposited in suitable places. 

Cephalization is carried to its maximum in this class, 
and we have animals of the highest instincts under the 
articulate type. The “brain” is formed of several gan¬ 
glia massed together, and lies across the upper side of the 
throat, just behind the mouth. The main cord lies along 
the ventral side of the body, with a swelling for each seg¬ 
ment; besides this, there is a visceral nerve representing, 
in function, the sympathetic system of Vertebrates. The 
digestive apparatus consists of a pharynx, gullet (to which 
a crop is added in the Fly, Butterfly, and Bee tribes), giz¬ 
zard, stomach, and intestine. There are no absorbent ves¬ 
sels, the chyme simply transuding through the walls of 
the canal. The blood, usually a colorless liquid, is driven 
by a chain of hearts along the back, i. e ., by a pulsating 
tube divided into valvular sacs, ordinarily eight, which 
allow the current to flow only towards the head. As it 
leaves this main pipe, it escapes into the cavities of the 
body, and thus bathes all the organs. Although the blood 
does not circulate in a closed system of blood-vessels, as in 
Vertebrates, yet it always takes one set of channels in go¬ 
ing from the heart, and another in returning. Respira¬ 
tion is carried on by tracheae, a system of tubes opening 
at the surface by a row of apertures (« piracies ), generally 
nine on each side of the body. 

The sexes are distinct, and the larvae are hatched from 
eggs. As a rule, an Insect, after reaching the adult, or 


294 


COMPARATIVE ZOOLOGY. 


imago, state, lives from a few hours to several years, and 
dies after the process of reproduction. Growth takes 
place only during larval life, and all metamorphoses occur 
then. Among the social tribes, as Bees and Ants, the 
majority (called “ workers”) do not develop either sex. 

Insects (the six-footed Arthropods) comprise nearly one 
half of the whole Animal Kingdom, or from one hundred 
and seventy thousand to two hundred thousand species. 
They are grouped into seven orders: 

Lower series: body usually flattened; prothorax large and 
squarish; mouth-parts usually adapted for biting; met¬ 
amorphosis often incomplete; pupa often active; larva 
flattened, often resembling the adult. 

Higher series: body usually cylindrical; prothorax small; 
mouth-parts more generally formed for sucking; meta¬ 
morphosis complete; pupa inactive; larva usually cylin¬ 
drical, very unlike the adult. 

1. Neuroptera have a comparatively long, slender body, 


Neuroptera , 
Orthoptera , 
Hemiptera , 
Coleoptera. 

Diptera, 

Lepidoptera, 

Hymenoptera. 



Pig. 263.— Dragon-fly ( Libellula). 

and four large, transparent wings, nearly equal in size, 
membranous and lace-like. Such are the brilliant Dragon* 



ARTIIROPODA. 


295 


flies, or Devil’s Darning-needles (. Libellula ), well known 
by the enormous head and thorax, large, prominent eyes 
(each furnished with twenty-eight thousand polished 
lenses), and Scorpion - like abdomen; the delicate and 
short-lived May-flies (Ephemera) \ Caddis-flies ( Phryga - 
nea ), whose larvae live in a tubular case made of minute 
stones, shells, or bits of wood; the Horned Corydalis 
(' Corydalus ), of which the male has formidable mandibles 
twice as long as the head; and the White Ants (Termes) 
of the tropics. 

2. Orthoptera have four wings: the front pair some¬ 
what thickened, narrow, and overlapping along the back; 
the hind pair broad, net-veined, and folding up like a fan 



Fig. 264.—Metamorphosis of a Cricket ( Gryllvs ). 


upon the abdomen. The hind legs are usually large, and 
fitted for leaping, all the species being terrestrial, although 
some fly as well as leap. The eyes are small, the mouth 
remarkably developed for cutting and grinding. The lar- 


296 


COMPARATIVE ZOOLOGY. 



Fig. 265.—Metamorphosis of an Hemipter, Water-boatman (Notonectcc). 


vae and pupae are active, and resemble the imago. They 
are nearly all vegetarian. Each family produces charac¬ 
teristic sounds (str id illation). The representative forms 



Fig. 266.—Seventeen-year Cicada {Cicada septendecim): a, pupa- b t 
the imago, c, has escaped through a rent in the back; d, holes in 
the eggs, e, are inserted. 


same, after 
twig, where 














ARTHROPODA. 


297 


are Crickets ( Gryllus), Locusts (. Locusta ), Grasshoppers 
(. Acrydium ), Walking- sticks (. Phasma), and Cockroaches 
(. Blatta ). 

3. Hemiptera, or “ Bugs,” are chiefly characterized by 
a suctorial mouth, which is produced into a long, hard, 
beak, in which mandibles and maxillae are modified into 
bristles and enclosed by the labium. The four wings are 
irregularly and sparsely veined, sometimes wanting. The 
body is flat above, and the legs slender. The larva differs 
from the imago in wanting wings. In some species the 
fore-wings are opaque at the base and transparent at 
the apex, whence the name of the order. Some feed on 
the juices of animals, others on plants. Here belong the 
wingless Bed-bug ( Cimex ) and Louse ( Pediculus ), the 
Squash-bug (Coreus), Water-boatman ( Notonecta ), Seven¬ 
teen-year Locust (Cicada), Cochineal (Coccus), and Plant- 
louse (Aphis). 

4. Coleoptera, or “ Beetles.” This is the largest of the 
orders, the species numbering about ninety thousand. 
They are easily recognized by the elytra, or thickened, 



Fio. 267.—a, imago, and b, larva, of the Goldsmith Beetle (Cotalpa lanigera ); c, 
pupa of June-bug ( Lachno&terna fmca). 


horny fore-wings, which are not used for flight, but serve 
to cover the hind pair. When in repose, these elytra are 
always united by a straight edge along the whole length. 
The hind wings, when not in use, are folded transversely. 




298 


COMPARATIVE ZOOLOGY. 


The mandibles are well developed, and the integument 
generally is hard. The legs are strong, for the Beetles 
are among the most powerful running Insects. The lar¬ 
vae are worm-like, and the pupa is motionless. The high¬ 
est tribes are carnivorous. The most prominent forms 



Fig. 268 — Sexton Beetles {Necruphorm vespillo), with larva and nymph. They are 
burying a mouse, preparatory to laying their eggs in it., 


are the savage but beautiful Tiger Beetles ( Cicindela ); 
the common Ground Beetles (Cardbus), whose hind wings 
are often absent; the Diving Beetles (. Dytiscus ), with 
boat-shaped body, and hind legs changed into oars; the 
Carrion Beetles (< Silphci ), distinguished by their black, flat 



ARTHROPODA. 


299 

bodies and club-shaped antennae; the Goliath Beetles 
(Scarabceus), the giants of the order; the Snapping-bugs 
( Elater ); the Lightning-bugs (Pyrophorus ); the spotted 
Lady-birds ( Coccinella ); the showy, Long-horned Beetles 



Fig. 269.— Metamorphosis of the Mosquito (Culex pipiens). 























































300 


COMPARATIVE ZOOLOGY. 


('Cerambycidce ); and the destructive Weevils (Curculio* 
nidce ), with pointed snouts. 

5. Dipiera , or “ Flies,” are characterized by the rudi¬ 
mentary state of the hinder pair of wings. Although 
having, therefore, but one available pair, they are gifted 
with the power of very rapid flight. While a Bee moves 
its wings one hundred and ninety times a second, and a 
Butterfly nine times, the House-fly makes three hundred and 
thirty strokes. A few species are wingless. The eyes are 
large, with numerous facets. In some forms, as the House¬ 
fly, all the mouth-parts, except the labium, are rudimen¬ 
tary ; and the labium has an expanded tip, by means of 



Fig. 270.—Metamorphosis of the Flesh-fly (Sarcophaga carnaria ); a, eggs; 6, you»<* 
maggots just hatched; c, d, full-grown maggots; e, pupa; /, imago. 


which the fly licks up its food. In other forms, as the 
Mosquito, the other mouth-parts are present as bristles or 
lancets, fitted for piercing; the thorax is globular, and the 
legs slender. The larvae are footless grubs. The Diptera 
number about twenty-four thousand. Among them are 
the Mosquitoes ( Culex ); Hessian-fly ( Cecidomyia ), so de¬ 
structive to wheat; Daddy-long-legs {Tipula), resembling 
a gigantic Mosquito; the wingless Flea (Pulex) ; besides 
the immense families represented by the House-fly {Mus¬ 
ed) and Bot-fly {CEstrus). 

6. Lepidoptera, or “ But¬ 
terflies” and “Moths,” are 
known chiefly by their four 
large wings, which are thick¬ 
ly covered on both sides by 

cFiq. 271 . —Scales from the Wings of vari- 0Verla PP in g Scales. 

ous Lepidoptera. The scales are of different 










ARTIIROPODA. 


301 



colors, and are often arranged in patterns of exquisite 
beauty. They are in reality modified hairs, and every 
family has its partic¬ 
ular form of scale. 

The head is small, 
and the body cylin¬ 
drical. The legs are 
not used for locomo¬ 
tion. All the mouth 
parts are nearly obso¬ 
lete except the maxil¬ 
lae, which are fash¬ 
ioned into a “ probos¬ 
cis ^ for pUinpinfiT up P IG -272.—Part of the Wing of a Moth ( Saturnia ), 
r r & r magnified to show the arrangement of scales. 

the nectar of flowers. 

The larvae, called “ caterpillars,” have a worm-like form, 
and from one to five pairs of abdominal legs, in addition 
to the three on the thorax. The mouth is formed for mas¬ 
tication, and (ex¬ 
cept in the larvae 
of Butterflies) the 
lip has a spinneret 
connected with silk- 
glands. 

There are three 
groups : the gay 
Butterflies, having 
knobbed or hooked 
antennae, and flying 
in the day only; 
the dull-colored Sphinges, with antennae thickened in the 
middle, and flying at twilight; and the nocturnal Moths, 
which generally prefer the night, and whose antennae are 
thread-like and often feathery. Generally, when at rest, 
the Butterflies keep their wings raised vertically, while 



Fig. 273.— Vanessapolyehloros, or “Tortoise-shell But¬ 
terfly.” 









302 


COMPARATIVE ZOOLOGY. 



Fig. 274.— Moth and Larva of Attacus pavonia-major. 


the others hold theirs horizontally. The pupa of the 
former is unprotected, and is usually suspended by a bit 
of silk : 163 the pupa of the Moths is enclosed in a cocoon. 



Fig. 275.—Fruit-moth (Carpocapsa pomonella): b, larva ; a, chrysalis; c, imago. 







ARTHROPODA. 


303 





From twenty-two tliousand to twenty-four thousand 
Lepidopterous species have been identified. Some of the 
most common Butterflies are the swallow-tail PapiUo, 
the white Pieris , the sulphur- 
yellow Colias; the Argynnis , 
with silver spots on the under 
side of the hind wings; the 
Vanessa , with notched wings. 

The Sphinges exhibit little 
variety. They have narrow, 
powerful wings, and are some¬ 
times mistaken for Humming- 
birds. The “ potato -worm ” 
is the caterpillar of a Sphinx. 

The most conspicuous Moths 
are the large and beautiful 
Attacus , distinguished by a 
triangular, transparent spot 
in the centre of the wing; 
the white Bombyx , or “ silk¬ 
worm the reddish-brown Clisiocamjpa , whose larva, “ the 
American Tent-caterpillar,” spreads its web in many an 
apple and cherry tree; the pale, delicate Geometrids; and 
the small but destructive Tineids , represented by the 
Clothes-moth. 

7. Hymenoptera , comprising at least twenty-five thou¬ 
sand species, include the highest, most social, and, we may 
add (if we except the Silk-worm), the most useful, of In¬ 
sects. They have a large head, with compound eyes and 
three ocelli, mouth fitted both for biting and lapping, 
legs formed for locomotion as well as support, and four 
wings equally transparent, and interlocking by small 
hooks during flight. The females are usually provided 
with a sting, or borer. The larvae are footless, helpless 
grubs, and generally nurtured in cells, or nests. Such are 


Fig. 2T6. — Head of a Caterpillar, from 
beneath: a , antennae; b, horny jaws; 
c, thread of silk from the conical fusu- 
lus, on either side of which are rudi¬ 
mentary palpi. 


304 


COMPARATIVE ZOOLOGY. 


the Honey-bees (Apis), Humble-bees (Bombus), Wasps 
(Vespa), Ants (Formica), Ichneumon-flies, and Gall-flies. 
Those living in societies exhibit three castes : females, or 
“ queens males, or “ drones and neuters, or sexless 
“ workers.” There is but one queen in a hive, and she 
is treated with the greatest distinction, even when dead. 
She dwells in a large, pear-shaped cell, opening down¬ 
ward. She lays three kinds of eggs: from the first 
come forth workers, the second produces males, and the 
last females. The drones, of which there are about eight 
hundred in an ordinary hive, are marked by their great 
size, their large eyes meeting on the top of the head, and 



a b c 

Fig. 277.—Honey-bee {Apis mellifim ): a, female; b, worker; c, male. 


by being stingless. The workers, which number twenty 
to one drone, are small and active, and provided with 
stings, and hollow pits in the thighs, called “ baskets,” 
in which they carry pollen. Their honey is nectar elabo¬ 
rated in the crop by an unknown process; while the wax 
is secreted from the sides of the abdomen and mixed with 
saliva. There is a subdivision of extra labor: thus there 
are wax-workers, masons, and nurses. Ants (except the 
Saiiba) have but two classes of workers. While Ants live 
in hollow trees or subterranean chambers (called formi- 
carium), Honey-bees and Wasps construct hexagonal cells. 
The comb of the Bee is hung vertically, that of the Wasp 
is horizontal. 


TUNICATA. 


305 


Snbkingdom VII. —Tunicata. 

This small and singular group of animals has relations 
with the worms on the one hand and with the Vertebrates 
on the other. The most common forms (the solitary As- 
cidians) are enclosed in a 
leathery, elastic bag, one end 
of which is fastened to the 
rocks, while the other has 
two orifices, for the inlet 
and exit of a current of 
water for nutrition and res¬ 
piration. They are without 
head, feet, arms, or shell. In¬ 
deed, few animals seem more Fiq - 278.—An Ascidian. 

helpless and apathetic than these apparently shapeless be¬ 
ings. The tubular heart exhibits the curious phenomenon 
of reversing its action at brief intervals, so that the blood 
oscillates backward and forward in the 
same vessels. Another peculiarity is the 
presence of cellulose in the skin. The 
water is drawn by cilia into a branchial 
sac, an enlargement of the first part of 
the intestine, whence it escapes through 
openings in the sides, to the excurrent ori¬ 
fice, while the particles of food drawn in 
with the water are retained and passed 
into the intestine. The larva is active, 
swimming by means of a long tail. It 
looks like a tadpole, and has a notochord 
and a nervous system closely resembling 
those of a Vertebrate. Afterwards it at- 

IO.z (if.—umgraiu ui oim- 

pie Ascidian: b,s, bran- taches itself by the head, the tail is ab- 

chial sac; n, nervous , . 

ganglion; s, stomach; i, sorbed, and the nervous system is re- 

thfoSli ;“k, heart a °' duced to a single small ganglion. 

20 







306 


COMPARATIVE ZOOLOGY. 


Subkingdom VIII.—Vertebrata. 

This grand division includes the most perfect animals, 
or such as have the most varied functions and the most 
numerous and complex organs. Besides the unnumbered 
host of extinct forms, there are about twenty-five thousand 
living species, widely differing among themselves in shape 
and habits, yet closely allied in the grand features of their 
organization, the general type being endlessly modified. 

The fundamental distinctive character of Vertebrates 
is the separation of the main mass of the nervous system 
v from the general cav¬ 

ity of the body. A 
transverse section of 
the body exhibits two 
cavities, or tubes—the 
dorsal, containing the 
cerebro-spinal nervous 
system ; the ventral, in¬ 
closing the alimentary 
canal, heart, lungs, and 
a double chain of gan¬ 
glia, or sympathetic 
system. This ven¬ 
tral, or haemal, cavity 
corresponds to the 

Fig. 280.—Ideal Plans of the Subkingdoms. F, * 

transverse section of vertebrate type ; v, the whole body of an In- 
same, inverted. M, transverse section of mol- , , ... , 

luscous type; and Md, of molluscoid. A and Vertebrate ; While the 
Ad, transverse sections of articulate type, high J nr{J i -nmiral ic 

and low. C, longitudinal section of ccelente- UUI or “CUrai, IS 

rate type; a, alimentary canal; c, body-cavity, added. 

In the other figures, the alimentary canal is 

shaded, the heart is black, and the nervous Vertebrates are also 
cords are open rings. .. J . . . , , 

distinguished by an in¬ 
ternal, jointed skeleton, endowed with vitality, and capa¬ 
ble of growth and repair. During embryo-life it is rep¬ 
resented by the notochord; but this is afterwards replaced 



VERTEBRATA. 


307 


by a more highly developed 

vertebral column of cartilage 

© 

or bone. The column and 
cranium are never absent in 
the eraniota; other parts may 
be wanting, as the ribs in Frogs, 
limbs in Snakes, etc . 154 The 
limbs are never more than 
four, and are always articu¬ 
lated to the haemal side of the 
body, while the legs of Inver¬ 
tebrates are developed from 
the neural side. The muscles 
moving the limbs are attached 
to the endoskeleton. 

The circulation of the blood 
is complete, the arteries being 
joined to the veins by capil¬ 
laries, so that the blood never 
escapes into the visceral cav¬ 
ity as in the Invertebrates. 
All have a portal vein, carry¬ 
ing blood through the liver; 
all have lacteals and lym¬ 
phatics. The blood is red, 
and contains both kinds of 
corpuscles . 155 The teeth are 
developed from the dermis, 
never from the cuticle, as in 
Mollusks and Articulates; the 
jaws move vertically, and are 
never modified limbs. The 
liver and kidneys are always 
present. The respiratory or¬ 
gans are either gills or lungs, 



Fio. 2S1. — Diagram of Circulation in 
the higher Vertebrates: 1, heart; 2, 
lungs; 3, head and upper extremities; 
4, spleen; 5, intestine; 6, kidney; 7, 
lower extremities; 8, liver. (From 
Dalton’s “Physiology.") 



308 


COMPARATIVE ZOOLOGY. 


or both. Vertebrates are the only animals which breathe 
through the mouth. 

The nervous system has two marked divisions: the 
cerebro-spinal, presiding over the functions of animal life 
(sensation and locomotion); and the sympathetic, which 
partially controls the organic functions (digestion, respi¬ 
ration, and circulation). In no case does the gullet pass 
through the nervous system, as in Invertebrates, and the 
mouth opens on the side opposite to the brain. Probably 
none of the five senses are ever altogether absent. The 
form of the brain is modified by the relative development 
of the various lobes. In the lower Vertebrates, the cere¬ 
bral hemispheres are small — in certain Fishes they are 
actually smaller than the optic lobes—in the higher, they 
nearly or quite overlap both olfactories and cerebellum. 
The brain may be smooth, as in most of the cold-blooded 
animals, or richly convoluted, as in Man. 

There is no skull in Amphioxus. In the Marsipo- 
branchii and Elasmobranchii it is cartilaginous. In other 
fishes it is cartilage overlaid with bone. In Amphibians 
and Keptiles, it is mingled bone and cartilage. In Birds 
and Mammals, mainly or wholly bony. The human skull 
contains fewer bones than the skull of most animals, ex¬ 
cepting Birds. The skull of all Vertebrates is divisible 
into two regions: the cranium, or brain-case, and the face. 
The size of the cranial capacity, compared with the area 
of the face, is generally the ratio of intelligence. In the 
lower orders, the facial part is enormously predominant, 
the eye-orbits are directed outward, and the occipital con¬ 
dyles are nearly on a line with the axis of the body. In 
the higher orders, the face becomes subordinate to the 
cranium, the sensual to the mental, the eyes look forward, 
and the condyles approach the base of the cranium. Com¬ 
pare the “ snouty ” skull of the Crocodile and the almost 
vertical profile of civilized Man. A straight line drawn 


VERTEBRATA. 


309 


from the middle of the ear to the base of the nose, and 
another from the forehead to the most prominent part of 
the upper jaw, will include what is called the facial an¬ 
gle, which roughly gives the relation between the two re¬ 
gions, and therefore the rank of the animal. 168 In the 
cold-blooded Vertebrates the brains do not fill the cranium; 
while in Birds and Mammals a cast of the cranial cavity 
well exhibits the general features of the cerebral surface. 167 

All Vertebrates are single and free. Mammals bring 
forth their young alive, having directly nourished them 
from the mother before birth (viviparous). In almost all 
the others the nourishment is laid up in the egg, which is 
laid before hatching ( [oviparous ), or is retained in the 
mother until hatched ( ovoviviparous ), as in some Reptiles 
and Fishes. 

There are two great divisions of the subkingdom, 
Acrania and Craniota , or Vertebrates without skulls and 
those with skulls. 

The Craniota are divided into five great classes: Fishes , 
Amphibians , Reptiles , Birds , and Mammals. The first 
three are “cold-blooded,” the other two are “warm¬ 
blooded.” Fishes and Amphibians have gills during the 
whole or a part of their lives, while the rest never have gills. 
Fishes and Amphibians in embryo have neither amnion 
nor allantois, while the other three are provided with both. 

There are three provinces of skull-bearing Vertebrates. 

Fishes and Amphibians agree in having gills, in want-. 
ing amnion and allantois, and in possessing nucleated red 
bl ood-corp uscles (Ichthyopsida). 

Birds and Reptiles agree in having no gills, but both 
amnion and allantois, in the articulation of the skull with 
the spine by a single condyle, in the development of the 
skin into feathers or scales, and in circulating oval, nucle¬ 
ated, red corpuscles ( Sauropsida). 

Mammals differ from Birds and Reptiles in having two 


310 


COMPARATIVE ZOOLOGY. 


occipital condyles, and their blood-corpuscles are not nu¬ 
cleated 169 {Mammalia). 


Division I.—Acrania. 
Vertebrates without a skull. 



Class.—P haryngobranchii. 

The Acrania are represented by 
the singular animal Amphioxus or 
Lancelet. It is about two inches long, 
semi-transparent, without skull, limbs, 
brain, heart, or red blood-corpuscles. 
It has for a skeleton a notochord only. 
It breathes by very numerous gill 
arches, without fringes, and the water 
is drawn in by cilia, which line the 
gill slits. The embryo develops into 
a gastrula closely resembling that of 
the Invertebrates. The animal lives 
in the sandy bottom of shallow parts 
of the ocean, and has been found in 
the Mediterranean Sea, in the Indian 
Ocean, and on the east coast of North 
and South America. 

Division II.—Craniota. 

Vertebrates with a distinct skull. 

Class I.—Pisces. 

Fishes are the lowest of Verte¬ 
brates. They fall far behind the rest 
in strength, intelligence, and sensi¬ 
bility. The eyes, though large, are 
almost immovable, bathed by no tears, 
and protected by no lids. Dwelling 
in the realm of silence, ears are little 




VERTEBRATA. 


311 


needed, and such as they have are without external parts, 
the sound being obliged to pass through the cranium. 
Taste and smell are blunted, and touch is nearly confined 
to the lips. 

The class yields to no other in the number and variety 
of its forms. It includes nearly one half of all the ver- 
tebrated species. So great is the range of variation, it is 
difficult to frame a definition which will characterize all the 
finny tribes. It may be said, however, that Fishes are the 
only backboned animals having median fins (as dorsal and 
anal) supported by fin-rays, and whose limbs (pectoral and 
ventral fins) do not exhibit that threefold division (as thigh, 
leg, and foot) found in all other Vertebrates. 159 

The form of Fishes is admirably adapted to the element 
in which they live and move. Indeed, Nature nowhere 
presents in one class such elegance of proportions with 
such variety of form and beauty of color. The head is 



Fig. 283.—Scales of Fishes: A, cycloid scale (Salmon); B, ctenoid scale (Perch); C, 
placoid scale (Ray); D, gauoid scales (Amblypteru$)—a t upper surface; b, under 
surface, showing articulating processes. 

disproportionately large, but pointed to meet the resist¬ 
ance of the water. The neck is wanting, the head be¬ 
ing a prolongation of the trunk. The viscera are closely 
packed near the head, and the long, tapering trunk is left 
free for the development of muscles which are to move 
the tail—the instrument of locomotion. The biconcave 
vertebrae, with intervening cavities filled with elastic gel¬ 
atine, are designed for rapid and versatile movements. The 
body is either naked, as in the Lamprey, or covered with 
f 


312 


COMPARATIVE ZOOLOGY. 


polished, overlapping scales, as in the Perch. Rarely, 
as in the Sturgeon, it is defended by bony plates, or by 
minute, hard spines, as in the Shark. Scales with smooth, 
circular outline are called cycloid ; those with notched or 
spiny margins are ctenoid. Enameled scales are ganoid , 
and those with a sharp spine, like those of the Shark, are 
placoid. 

The vertical fins (dorsal, anal, and caudal) are peculiar 
to Fishes. The dorsal vary in number, from one, as in 
the Herring, to three, as in the Cod; and the first dorsal 
may be soft, as in the Trout, or spiny, as in the Perch. 



Fig. 2S4.—Blue-fish (Temnodon saltator). All seas. 


If the dorsals are cut off, the Fish reels to and fro. The 
caudal may be homocercal, as in ordinary species; or het- 
erocercal, as in Sharks. In ancient heterocercal Fishes, 
the tail was frequently vertebrated. The pectoral and 
ventral fins stand for the fore and hind limbs of other 
Vertebrates. As the specific gravity of the body is greater 
than that of the water, most Fishes are provided with 
an air-bladder,which is an outgrowth from the oesopha¬ 
gus. This is absent in such as grovel at the bottom, as 
the Rays, and in those, like the Sharks, endowed with 
compensating muscular power. 

Fishes have no prehensile organ besides the mouth. 
Both jaws are movable. The teeth are numerous, and 


VERTEBKATA. 


313 


may be recurved spines, as in the Pike; flat and triangu¬ 
lar, with serrated edges, in the Shark; or flat and tessel¬ 
lated in the Ray. They feed principally on animal mat¬ 
ter. The digestive tract is relatively shorter than in other 
Vertebrates. 169 The blood is red, and the heart has rarely 
more than two cavities, an auricle and a ventricle, both on 
the venous side. Ordinary Fishes have four gills, which 
are covered by the operculum , and the water escapes from 
an opening behind this. In Sharks there is no operculum , 



Fig. 2S5.—Salmon (Salmo salar). Both hemispheres. 


and each gill opens separately. The brain consists of sev¬ 
eral ganglia placed one behind the other, and occupies but 
a small part of the cranial cavity. Its average weight to 
the rest of the body may be as low as 1 to 3000. The 
eggs of bony Fishes are naked and multitudinous, some¬ 
times numbering millions in a single spawn ; those of the 
Sharks are few, and protected by a horny shell. 

There are about thirteen thousand species of Fishes, of 
which over two thirds are Teleostei. There are two sub- 
classes of Pisces. 



314 


COMPARATIVE ZOOLOGY. 


Subclass I.— Marsipobranchii. 



The Lampreys and Hag-fish have a persistent noto¬ 
chord, a cartilaginous 
skull, no ldwer jaw, 
a round, suctorial 
mouth, horny teeth, 
one nasal-organ, no 
scales, limbs, or gill- 
arches. The gills are 
pouch-like (whence 
the name of the class), and open separately. They are 
found both in salt and fresh water. 


Fio. 2S6.—Lamprey (Petromyzon Aviericanw). At¬ 
lantic. 


# 


Subclass II.— Pisces Proper. 

The true Fishes have two nasal organs, and well-devel¬ 
oped jaws and gill-arches. There are four orders: 

1. Elasmobranchii , having a cartilaginous skeleton, and 
a skin naked or with placoid scales. The gill-openings are 
uncovered; and the mouth is generally under the head. 
The ventral fins are placed far back; the pectorals are 
large, in the Eays enormously developed; and the tail is 
heterocercal. Such are the Sharks, Eays, and Chimaera. 



Fig. 2S7.—Shark (Carcharias vulgaris). Atlantic. 






VERTEBRATA. 




315 

They are all marine. The largest Shark found, and there¬ 
fore the largest Fish, measured forty feet in length. 


2. Ganoidei , distinguished by their enameled scales or 
bony plates. The endoskeleton is usually not completely 
ossified; the ventral fins are placed far back; and the 
tail is generally heterocercal. The gills are like those of 
the bony Fishes, and the air-bladder has a duct, and may 
aid in respiration. This was one of the largest orders in 
old geological history. The few modern representatives, 
as the Sturgeon, Gar-pike, Mud (or Dog) Fish, and Polyp- 
terus , are essentially 
fresh-water. 

3. Teleostei , in¬ 
cluding all the com¬ 
mon Fishes having 

a bony endoskeleton Fig. 289.—Gar-pike (Lepidos'eusosseus). LakeOntario 


Fig. 2S8.—Thornback (Raid clavata). European seas. 




316 


COMPARATIVE ZOOLOGY. 




American rivers. 


jfiG. 290 _Sturgeon (Acipemser sturio). Atlantic coast. 

and a scaly exoskeleton. The skull is extremely com¬ 
plicated ; the upper and lower jaws are complete, and the 

gills are comb-like 
or tufted. The tail 
is homocercal; the 
other fins are varia¬ 
ble in number and 
Fig. 291.— (Jut-nou, ur jL.on.ea Fout ( Pimeludm catus). position. In the 

soft - finned Fishes, 
the ventrals are ab¬ 
sent, as in the Eels; 
or attached to the 
abdomen, as in the 
Salmons, Herrings, 

Fig. 292.— Cod (Morrhua Americana). Atlantic coast. T .~ 

Pikes,and Carps; or 
placed under the throat, as in the Cod, Haddock, and 
Flounder. In the spiny-finnfed Fishes, the ventrals are 
generally under or in front of the pectorals, and the scales 
ctenoid, as in the Perches, Mullets, and Mackerels. 

4. Dijpnoi. These Fishes connect the class with the 
Amphibia. They have an eel-like body, covered with 
cycloid scales; an embryonic notochord for a back-bone; 




Fig. 293. —Protopterus annectem; one fourth natural tuze. African rivers. 



VERTEBRATA. 


317 

long, ribbon-like pectoral and ventral fins, set far apart; 
two auricles, and one ventricle; and, besides gills, a cellu¬ 
lar air-bladder, which is used as a lung. 

The representatives are Ceratodus from Australia, Pro- 
topterus from Africa, and Lepidosiren from Brazil. 

Class II. —Amphibia. 

These cold-blooded Vertebrates are distinguished by 
having gills when young, and true lungs when adult. 
They have no fin-rays, and the limbs, when present, have 
the same divisions as those of higher animals. The skin 
is soft, and generally naked, and the skeleton is ossified. 
The skull is flat, and articulates with the spinal column 
by two condyles. There is no distinct neck; and the ribs 
are usually small or wanting. The heart consists of two 
auricles and one ventricle. All undergo metamorphosis 
upon leaving the egg, passing through the “ tadpole” state. 
They commence as water-breathing larvse, when they re¬ 
semble Fishes in their respiration, circulation, and locomo¬ 
tion. In the lowest forms, the gills are retained through 
life; but all others have, when mature, lungs only, the 
gills disappearing. The cuticle is frequently shed, the 
mode varying with the habits of the species. 161 The com¬ 
mon Frog, the type of this class, stands intermediate be¬ 
tween the two extremes of the vertebrate series; no fun¬ 
damental part is excessively developed. 

There are about four 
hundred and fifty liv¬ 
ing species, grouped 
in four orders: 

1. Urodela have a 
naked skin, a tail, and 
two or four limbs. 

Some retain their gills 

. . ..» ,, Fig. 294.— Head and Gills of Menobranchus. Cayuga 

through life, as the Lake. 



318 


COMPARATIVE ZOOLOGY. 


Proteus of Austria, Menobranchus of the eastern United 
States, and the two-legged Mud-eel {Siren) of South Car¬ 
olina. Others drop their gills, and always have four limbs, 
as the aquatic Newts and land Salamanders. 162 The fore 
limbs first make their appearance in the tadpole. 

2. Labyrinthodontia , now extinct, resembled gigantic 
Salamanders, except in their complex teeth and exoskele¬ 
ton of bony plates. 

3. Ccecilia have neither tail nor limbs, a snake-like form, 



Fig. 295.— Proteus anguinus. Europe. 


minute scales in the skin, and well-developed ribs. They 
are confined to the tropics. 

4. Batracliia include all the well-known tailless Am¬ 
phibians, as Frogs 
and Toads. They 
have a moist, naked 
skin, ten vertebrae, 
and no ribs. As they 

Fig. 296.—Red Salamander ( Pseudotriton ruber). breathe bv SWalloW- 

United States. . / 

ing the air, they can 
be suffocated by holding the mouth open. They have 







VERTEBRATA. 


319 


# v 

four limbs—the hinder the longer, and the first developed. 
They have four fingers and five toes. The tongue is long, 
and, fixed by its an¬ 
terior end, it can be 
rapidly thrown out as 
an organ of prehen¬ 
sion . 163 The eggs are 
laid in the water en¬ 
veloped in a glairy 
mass; and the tadpoles FlG ' 297 — Fr °s (**“"*>• 

resemble the Urodelans, till both gills and tail are absorbed. 
Frogs (Rand) have teeth in the upper jaw, and webbed 
feet; Toads (Bufd) are higher in rank, and have neither 
teeth nor fully webbed feet. The former have been 
known to live sixteen years, and the latter thirty-six. 

Class III. —Reptilia. 

These air-breathing, cold-blooded Vertebrates are dis¬ 
tinguished from all Fishes and Amphibians by never hav¬ 
ing gills, and from Birds by being covered with horny 
scales or bony plates. The skeleton is never cartilaginous; 
and the skull has one occipital condyle. The vertebrae are 
ordinarily concave in front; and the ribs are well devel¬ 
oped. With few exceptions, all are carnivorous; and teeth 
are always present, except in the Turtles, where a horny 
sheath covers the jaws. The teeth are never fastened in 
sockets, except in Crocodiles. The jaws are usually very 
wide. The heart has three chambers, save in Crocodiles, 
where the ventricle is partitioned. But in all cases a 
mixture of arterial and venous blood is circulated. The 
lungs are large, and coarsely cellular. The limbs, when 
present, are provided with three or more fingers as well 
as toes. 

There are about fifteen hundred species and four 
orders of living Beptiles : the first two have horny 



3-20 


COMPARATIVE ZOOLOGY. 


scales, the others have bony plates combined with 
scales. 

1. Ophidia , or Snakes, are characterized by the absence 
of visible limbs; 164 by the great number of vertebrae, 
amounting to over four hundred in the great Serpents; 
by a corresponding number of ribs, but no sternum; and 
no true eyelids, the eyes being covered with a transparent 



Fig. 298— Adder, or Viper (Pelias berm). England. 


skin. The tongue differs from that of nearly all other 
Reptiles in being bifid and extensile. The mouth is very 
dilatable. The skin is frequently shed, and always by re¬ 
versing it. Snakes make their way on land or in water 
with equal facility. 

As a rule, the venomous Snakes, as Vipers and Rattle¬ 
snakes, are distinguished by a triangular head covered with 
small scales; a constriction behind the head; two or more 
fangs, and few teeth; small eyes, with vertical pupil; and 
short, thick tail. In the harmless Snakes, the head gradu¬ 
ally blends with the neck, and is covered with plates; the 
teeth are comparatively numerous in both jaws; the pu- 


VERTEBRATA. 


321 



Fig. ‘299. — a, Head of a Harmless Suake (upper view); b , heads of various Venomous 

Snakes. 


pil is round, and the tail tapering. This rule, however, 
has many exceptions. 

2. Lacertilia , or Lizards, may be likened to Snakes pro¬ 
vided with four limbs, each having five digits. 165 The 
bod} 7 is covered with horny scales. All have teeth, which 
are simple in structure; and the halves of the lower jaw 
are firmly united in front, while those of Snakes are 



Fig. 300.—Lizard ( Lacerta). 
21 




322 


COMPARATIVE ZOOLOGY. 


loosely tied together by ligaments. Nearly all have a 
breast-bone, and the eyes (save in the Gecko) are fur¬ 
nished with movable lids. In the common Lizards and 
Chameleon, the tongue is extensile. The tail is usually 
long, and in some cases each caudal vertebra has a divis¬ 
ion in the middle, so that the tail, when grasped, breaks 
off at one of these divisions. The Chameleon has a pre¬ 
hensile tail. The Iguana is distinguished by a dewlap on 
the throat and a crest on the back. Except some of the 
Monitors of the Old World, all the Lizards are terrestrial. 

3. Chelonia, or Tortoises and Turtles, are of anomalous 
structure. The skeleton is external, so as to include not 
only all the viscera, but also the whole muscular system, 
which is attached internally; and even the limbs are 



Fig. 301— Hawk’s-bill Turtle (Eretmochelys imbricata). Tropical Atlantic. 

inside, instead of outside, the thorax. The exoskeleton 
unites with the endoskeleton, forming the carapace , or 
case, in which the body is enclosed. The exoskeleton con¬ 
sists of horny plates, known as “ tortoise-shell ” (in the 
soft Tortoises, Trionyx , this is wanting), and of dermal 










VERTEBRATA. 


323 



-Box-tortoise (Citstudo Virginea). United 
States. 


bones, united to the expanded spines of the vertebrae and 
to the ribs, making the walls of the carapace. The ven¬ 
tral pieces form the 
plastron , or ster¬ 
num. 166 All are 
toothless. There 
are always four stout 
legs; and the order 
furnishes the only 
examples of Verte- FlG . 30 2 . 
brates lower than 
Birds that really walk, for Lizards and Crocodiles wrig¬ 
gle, and drag the body along. There are no teeth, but a 
horny beak. The eggs are covered with a calcareous 
shell. 

The Sea-turtles, as the edible Green Turtle and the 
Hawk’s-bill Turtle, which furnish the “tortoise-shell” 
of commerce, have the limbs converted into paddles. The 
fresh-water forms, represented by the Snapping Turtle 
( Chelydra ), are amphibious, and have palmated feet. Land 
Tortoises ( Testudo ) have short, clumsy limbs, fitted for 
slow motion on the land; the plastron is very broad, and 
the carapace is arched (while it is flattened in the aquatic 
species), and head, legs, and tail can be drawn within it. 
The land and marine species are vegetable-feeders; the 
others, carnivorous. 

4. Crocodilia, the highest and largest of Reptiles, h|ve 
also two exoskeletons—one of horny scales (epidermal), and 
another of bony plates (dermal). The bones of the skull 
are firmly united, and furnished with numerous teeth, im¬ 
planted in distinct sockets. The lower jaw extends back 
of the cranium. The heart has four cavities, but the pul¬ 
monary artery and aorta communicate with each other, so 
that there is a mixture of venous and arterial blood. 
They have external ear-openings, closed by a flap of the 




32tt 


COMPARATIVE ZOOLOGY. 


skin, and eyes with movable lids; a muscular gizzard; a 
long, compressed tail; and four legs, with feet more or 
less webbed, and having five toes in front and four be¬ 
hind. The existing species are confined to tropical rivers, 
and are carnivorous. The eggs are covered with a hard 
shell. 

There are three representative forms: the Gavial of the 
Ganges, remarkable for its long snout and uniform teeth; 
the Crocodiles, mainly of the Old World, whose teeth are 
unequal, and the lower canines fit into a notch in the edge 
of the upper jaw, so that it is visible when the mouth is 



Fig. 303. —Alligator {A. Mississippiensis ). Southern States. 


closed; and the Alligators of the New World, whose ca¬ 
nines, in shutting the mouth, are concealed in a pit in the 
upper jaw. The toes of the Gavials and Crocodiles are 
webbed to the tip; those of the Alligators are not more 
than half-webbed. 

In the mediaeval ages of geological history, the class of 
Reptiles was far more abundantly represented than now. 
Among the many forms which geologists have unearthed 
are numerous gigantic Saurians, w T hich cannot be classi¬ 
fied with any of the four living orders. Such are the 
Ichthyosaurus , Plesiosaurus , Pterodactyle , Megalosaurus , 
and Iguanodon. 








VERTEBRATA. 


325 


Class IV. —Aves. 

Birds form the most clearly defined class in the whole 
Animal Kingdom. The Eagle and Hummer, the Ostrich 
and Duck, widely as they seem to be separated by size, 
form, and habits, still exhibit one common type of struct¬ 
ure. On the whole, Birds are more closely allied to Rep- 
tiles than to Mammals. In number, they approach the 
Fishes, ornithologists having determined eight thousand 
species, or more. 

A Bird is an air-breathing, egg-laying, warm-blooded, 
feathered Vertebrate, with two limbs (legs) for perching, 
walking, or swimming, and two limbs (wings) for flying 
or swimming. Organized for flight, it is gifted with a 
light skeleton, very contractile muscular fibre, and a res¬ 
piratory function of the highest development. 

The skeleton is more compact than those of Reptiles 
and Mammals, at the same time that it is lighter, and the 
bones are harder and whiter. It contains fewer bones 
than usual, many parts being anchylosed together, as the 
skull-bones, the dorsal vertebrae, and bones of the tarsus 
and metatarsus. The lumbar vertebrae are united to the 
ilia. The neck is remarkably long (containing from nine 
to twenty-four vertebrae) and flexible, enabling the head 
to be a most perfect prehensile organ. The ribs are gen¬ 
erally jointed in the middle, as well as with the backbone 
and sternum. The last, where the muscles of flight orig¬ 
inate, is highly developed. The skull articulates with 
the spinal column by a single condyle, and with the lower 
jaw, not directly, as in Mammals, but through the inter¬ 
vention of a separate bone, as in Keptiles. 

All Birds always have four limbs, while every other 
vertebrate class shows exceptions. The fore-limbs are fit¬ 
ted for flight. They ordinariiy consist of nine separate 
bones, and from the hand, fore-arm, and humerus are de- 


326 


COMPARATIVE ZOOLOGY. 


veloped the primary, secondary, and tertiary feathers of 
the wing. The hind-limbs are formed for progression— 
walking, hopping, running, paddling, and also for perch¬ 
ing and grasping. The modifications are more numerous 
and important than those of the bill, wing, or tail. There 
are twenty bones ordinarily, of which the tibia is the prin¬ 
cipal ; but the most characteristic is the tarso-metatarsus, 

which is a fusion of 
the lower part of the 
tarsus with the meta¬ 
tarsus. The rest of the 
tarsus is fused with 
the tibia. The thigh 
is so short that the 
knee is never seen out¬ 
side of the plumage; 
the first joint visible 
is the heel. 167 Most 
Birds have four toes 
(the external or “ lit- 

Fig. 304.—Principal Parts of a Bird: a, primaries; . ,, . . 

b, secondaries ; c, spurious wing; d, wing-coverts ; tie toe IS always 

e, tertiaries; /, throat, or jugulum; g , chin; h, wan ti no A . m an v ha VP 
bill; the meeting-line between the two mandi- wanting; , many nave 

bles is the commissure; the ridge on the upper three the hallux or 
mandible is called culmen; that of the lower, ’ J 

gonys; the space between the base of the npper “big” toe, being ab- 
mandible and the eye is the lore; i, forehead; k, & 

crown; l, scapular feathers; m, back; n, meta- Sent J while the US- 
tarsus, often called tarsus or tarso-metatarsus; , . i * K t t 
o, abdomen; p, rump; q, upper tail-coverts; r, ^llCU Las Dllt tWO, an- 

lower taii-coverts. swering to the third 

and fourth. The normal number of phalanges, reckoning 
from the hallux, is 2, 3, 4, 5. The toes always end in 
claws. 

Birds have neither lips nor teeth, epiglottis nor dia¬ 
phragm. The teeth are wanting, because a heavy masti¬ 
cating apparatus in the head would be unsuitable for 
flight. The beak, crop, and gizzard vary with the food.' 1 
It is a peculiarity of all Birds, though not confined to 



















VERTEBRATA. 


327 

them, that the generative products and the refuse of di¬ 
gestion are all discharged through one common outlet. 

The sole organs of prehension are the beak and feet. 
The circulation is double, as in Mammals, starting from a 
four-chambered heart. Respiration is more complete 
than in other Vertebrates. The lungs are fixed, and com¬ 
municate with air-sacs in various parts of the body, as 
along the vertebral column, and also with the interior of 
many bones, as the humerus and femur, which are usu¬ 
ally hollow and marrowless. 168 Both brain and cord are 
much larger relatively than in Reptiles; the cranium is 
larger in proportion to the face; and the parts of the brain 
are not situated in one plane, one behind the other. The 
cerebrum is round and smooth, and the cerebellum single- 
lobed. The ears resemble those of Crocodiles; but the 
eyes are well developed, and protected by three lids. They 
are placed on the sides of the head, and the pupil is al¬ 
ways round. The sexes generally differ greatly in plu¬ 
mage, in some cases more widely than two distinct species, 
but the coloration of either sex of any one species is very 
constant. 

There are two subclasses. 161 

Subclass I.— Ratitae {Cursores). 

This small and singular group is characterized by hav¬ 
ing no keel on the breastbone, rudimentary wings, feath¬ 
ers with disconnected barbs, and stout legs. The African 
Ostrich has two toes, the Cassowary three, and the Apte¬ 
ryx four. 

Its representatives are the Ostrich (> Struthio) of Africa 
and Arabia, South American Ostrich (Rhea\ Cassowary 
{Casuarius) of the East Indian Archipelago and Austra¬ 
lia, Emu {DromcBus) of Australia, and Apteryx , or Kiwi- 
kiwi, of New Zealand. Besides these, there are extinct 
gigantic forms from Madagascar Rpyornis) and from 


328 


COMPARATIVE ZOOLOGY. 


New Zealand ( Di- 
nornis , or Moa). 
This singular ge¬ 
ographical distri¬ 
bution, like that 
of the Dipnoi and 
Marsupials, shows 
that the group was 
once widely spread 
over the earth, but 
is now greatly re¬ 
stricted in area. 

Subclass II. 

Carinatae. 
Birds with a 
keeled sternum, 
and with devel¬ 
oped functional wings. 

A. Aquatic Birds. —Specially organized for swimming; 
the body flattened, and cov¬ 
ered with water-proof cloth¬ 
ing—feathers and down ; the 
legs short (the knees being 
wholly withdrawn within the 
skin of the body), and set far 
apart and far back; the feet 
webbed,and hind-toe elevated 
or absent. The legs are al¬ 
ways feathered to the heel at 
least. They are the only Birds 
whose neck is sometimes 
longer than the legs. 

1. Pygopodes , or Divers.— 

These lowest of the feathered 



Fid. 306.—Penguin (Aptenodytes Pennan ■ 
tii). Falkland Islands. 



Fig. 305.—African Ostrich (Struthio camelus). 



VERTEBRATA. 


329 



Fig. 307.—Loon (Colymbus torquatm). North America. 


tribe have very short wings and tail, and the legs are 
placed so far back that they are obliged, when on land, to 
stand nearly bolt upright. They are better fitted for div¬ 
ing than for flight, or even swimming. They belong to 
the high latitudes, living on Fishes mainly, and are repre¬ 
sented by the Penguins, Auks, Loons, and Grebes. 

2. Longipennes , or Gulls.—Distinguished by their long, 



Fig. 30S.—Tern (Sterna). 










330 


COMPARATIVE ZOOLOGY. 



Fig. 309. —Cormorant (Graculvs). 


pointed wings, usually long tail, and by great powers of 
flight. They are all carnivorous. Such are the Gulls and 
Terns, which frequent the sea-coast, lakes, and rivers; and 



the Albatrosses and Pe¬ 
trels (the largest and 
smallest of web-footed 
Birds), which are oce¬ 
anic. 

3. Totijpalmates , or 
Cormorants.—Charac¬ 
terized by a long bill, 
generally hooked; 
wings rather long; and 
toes long, and all four 
joined together by 
broad webs. Throat 
generally naked, and 
furnished with a sac. The majority are large sea-birds, 


Fig. 310.—Wild Goose (Bernicla Canadiensits). 
United States. 












VERTEBRATA. 


331 


and feed on Fishes, Mollusks, and Insects. Examples are 
the Cormorants, Pelicans, and Gan nets. 

4. Lamellirostres , or Ducks, have a heavy body, moder¬ 
ate wings, short tail, flattened bill, covered by a soft skin. 



Fig. 311. —Wild Duck (Anas boschas). North America. 



with ridges along the edges. Diet more commonly vege¬ 
tarian than animal. The majority inhabit fresh water— 
as the Ducks, Geese, Swans, and Flamingoes. 

B . Terrestrial 
Birds. —This group 
exhibits great diver¬ 
sity of structure; but 
all agree in being es¬ 
pecially terrestrial in 
habit, spending most 
of the time on the 
ground, not on trees 
or the water, al¬ 
though many of them 

fly and swim well. Fig. 312.— Sandpiper (Tringa hypoleuca). England. 





332 


COMPARATIVE ZOOLOGY. 



- A^WAv 


The legs are long or strong, and the knee is free from the 

body. The hind 
toe, when present, 
is small and ele¬ 
vated. 

5. Grallatores, or 
Wader s.—These 
are readily distin¬ 
guished by their 
long and bare legs. 
Generally, also, the 
toes, neck, and bill 
are of proportion¬ 
ate length, and the 
tail short. They 
feed on small ani¬ 
mals, and, with a 
few exceptions, fre¬ 
in flying, their legs are 
stretched out behind, while in most other Birds they are 
folded under the body. 

Such are the Rails, 

Cranes, Herons, Storks, 

Ibises, Stilts, Snipes, 

Sandpipers, and Plov¬ 
ers. 

6. Rasores , or Scratch¬ 
es.— As a rule, this 
order, so valuable to 
Man, is characterized 
by a short, arched bill; 
short and concave 

wings, unfitted for pro- Flo . S n._ RaU . or Marsh Hen (Kailua 
tracted flight; Stout United States. 

legs, of medium length; and four toes, the three in front 


Fig. 313.—Heron ( Ardea). 

quent the banks of rivers. 





VERTEBRATA. 


333 




Pig. 815.—Prairie-chicken (Cupidonia cupido). 
Western prairies. 


being united by a short web, and terminating in blunt 
claws. The legs are usually feathered to the heel, some¬ 
times (as in Grouse) 
to the toes. The 
feathers of the body 
are large and coarse. 

The males generally 
have gay plumage, 
and some appendage 
to the head. The 
nostrils are covered 
by a scale or valve. 

Their main food is 
grain. Such are the 
Grouse, Partridges, Turkeys, Pheasants, Poultry, and Cu¬ 
rasao ws. To these may be added, 

T. Columbm, or Pigeons and Doves, although they stand 

intermediate between the 
terrestrial and perching 
Birds, as the Flamingoes 
link the aquatic and terres¬ 
trial. They differ from the 
typical Rasores in having 
wings for prolonged flight, 
and slender legs, fitted rath¬ 
er for an arboreal life, with 
toes not united, and the 
hind toe on a level with 
the rest. 

C. Aerial Birds. —This 
highest and largest group 
includes all those Birds 
whose toes are fitted for grasping or perching, the hind 
toe being on a level with the rest. The knee is free from 
the body, and the leg is generally feathered to the heel. 


Fig. 316 .— Ring-dove (Columba palumbus). 
England. 






Fig. 319.—Golden Eagle (Aquila chrysaetos). North America and Europe 


334 COMPARATIVE ZOOLOGY. 


The wings are adapted for rapid or long flight; and they 
hop, rather than walk, on the ground. 170 They always 
live in pairs; and the young are hatched helpless. 

8. Eaptores , or Birds of Prey, differ from all other 
Birds, except Parrots, in having a 
strongly hooked bill and a waxy 
membrane (cere) at the base of the 
upper mandible; and from Parrots, 


Fig. 317—Barn-owl (Strix flam- 
mea ). Both hemispheres. 


Fig. 318. — Fish - hawk (Pandion Caroline.hsis ). 
United States. 


in having three toes in front and one behind. The toes 
are armed with long, strong, crooked talons; the legs are 
robust; and the wings are of considerable size, adapted 


VERTEBRATA. 


335 

for rapid and powerful flight. The bill is stout and sharp, 
and usually toothed. All are carnivorous. The female is 
larger than the male, except the Condor. There are two 



Fig. 320.—Foot of Parrot and Woodpecker. 


sections: the Diurnal , whose eyes are on the sides of the 
head, wings pointed, and metatarsus and toes covered over 
with scales, as the Vultures, Kites, Hawks, Falcons, and 
Eagles; the Nocturnal , whose large eyes are directed for¬ 
ward, and surrounded by radiating feathers, metatarsus 
feathered, and plumage soft, as the Owls. 

9. Picarice .—This polymorphic group has hardly any 
peculiarities in common. 171 The toes are usually paired, 
two in front and two behind. 

There are three divisions of the order: Cypseli , or 
Swifts, Goat-suckers, and Humming-birds; Cuculi , or 
Cuckoos, Kingfishers, Trogons, Toucans, Hornbills, and 
Hoopoes ; and Pici, or Woodpeckers. These Birds are not 
musical, and only ordinary fliers. They feed on Insects 
or fruit. The majority make nests in the hollows of old 
trees; but the Cuckoos lay in the nests of other Birds. In 
climbing, the Woodpeckers are assisted by their stiff tail. 



336 


COMPARATIVE ZOOLOGY. 





Fig- 321 .—Trogon elegam. Central America. 




VERTEBRATA. 


337 




10. Psittaci , or Parrots.—These birds have a strong, 
arched upper bill, with a cere at the base, a fleshy, thick. 


Fig. 323.—Goat-sucker ( Caprimulgm ). 
22 


and movable tongue, and paired toes. They have, usual¬ 
ly, brilliant plumage. They live in trees and feed on 
fruits. Such are the Parrots, Paroquets, and Cockatoos. 
11. Insessores , or Perchers.—This order is the most nu- 


Fig. 322— Head of a Fly-catcher ( Tyrannus ). 


338 


COMPARATIVE ZOOLOGY. 





Fig. 324 .— White-throated Sparrow (Zonotrichia 
albicollis). United States. 


merous and varied in the whole class. It comprehends all 
those tribes which live habitually among trees, excepting 

the Rapacious and 
Climbing Birds, and 
whose toes — three 
in front, and one be¬ 
hind—are eminently 
fitted for perching 
only. The legs are 
slender, and seldom 
used for locomo¬ 
tion. 

They are divisible 
into two sections : 

a. Clamatores , with 
nothing in common 
but a harsh voice. In 
most, the tarsus is 
enveloped in a row 
of plates, which meet 
behind in a groove, 
and the bill broad, 
and bent down ab¬ 
ruptly at the tip. 
The typical repre¬ 
sentatives are the 
Tyrant Fly-catchers. 

b. Oscines, or Song¬ 
sters, all of whom 
have a vocal appara¬ 
tus, though all do 
not sing. The an¬ 
terior face of the 

tarsus is one continuous plate, or divided transversely 
into large scales; and the plates on the sides meet be- 


Fio. 325.—Redstart (Setophaga rwticilla). Uuited 
States. 


Fig. 326.— White-eyed Vireo (Vireo Noveboracensis). 
United States. 




VERTEBRATA. 


339 


hind in a ridge. The toes, always three in front and 
one behind, are on the same level. The eggs are usu- 



Fig. 327—Kingfisher (Ceryle). 


ally colored. Here belong the Kavens, Crows, Jays, Birds- 
of-Paradise, Blackbirds, Orioles, Larks, Sparrows, Tan- 



Fig. 328. — Swallow ( Hirundo ). 


















340 


COMPARATIVE ZOOLOGY. 


agers, Wax-wings, Swallows, Wrens, Warblers, Thrashes, 
etc. 

Class V.— Mammalia, 

Mammals are distinguished from all other Vertebrates 
by any one of the following characters: they suckle their 
young; the thorax and abdomen are separated by a per¬ 
fect diaphragm; the red corpuscles of the blood have no 
nucleus, and are therefore double-concave; and either a 
part or the whole of the body is hairy at some time in 
the life of the animal. 173 

They are all warm-blooded Vertebrates, breathing only 
by lungs, which are suspended freely in the thoracic cav¬ 
ity ; the heart is four-chambered, and the circulation is 
double, as in Birds; the aorta is single, and bends over 
the left bronchial tube; the large veins are furnished with 
valves; the red corpuscles differ from those of all other 
Vertebrates in having no nucleus and in being circular 
(except in the Camel); the entrance to the windpipe is 
always guarded by an epiglottis; the cerebrum is more 
highly developed than in any other class, containing a 
greater amount of gray matter and (in the higher orders) 
more convolutions; the cerebellum has lateral lobes, a 
mammalian peculiarity, and there is a corpus callosum 
and a pons varolii; the cranial bones are united by 
sutures, and they are fewer than in cold-blooded Verte¬ 
brates ; the skull has two occipital condyles, a feature 
shared by the Amphibians; the lower jaw consists of 
two pieces only (often united), and articulates directly 
with the cranium; with four exceptions there are always 
seven cervical vertebrae ; 173 the dorsal vertebrae, and there¬ 
fore the ribs, vary from ten to twenty-four; the lumbar 
vertebrae number from two to nine ; the sacral from three 
to nine, and the caudal from two to forty-six ; the articu¬ 
lating surfaces of the vertebrae are generally flat; the 
fore-limbs are never wanting, and the hind-limbs only in 


VERTEBRATA. 


341 


a few aquatic forms; excepting the Whales, each digit car¬ 
ries a nail, claw, or hoof; the teeth (always present, save 
in certain low tribes) are planted in 
sockets; the mouth is closed by flexi¬ 
ble lips; an external ear is rarely ab¬ 
sent ; 174 the eyes are always present, 
though rudimentary in some burrow¬ 
ing animals ; they are viviparous ; 
and, finally, and perhaps above all, 
while in all other animals the embryo 
is developed from the nourishment 
laid up in the egg itself, in Mammals 
it draws its support, almost from 
the beginning, directly from the 
parent, and, after birth, it is sus¬ 
tained for a time by the milk se¬ 
creted by the mammary glands. 
From the first, therefore, till it can 
care for itself, the young Mam¬ 
mal is in vital connection with the 
parent. 

a h 


Pig. 329.—Longitudinal Section 
of Human Body (theoretical): 
a, cerebro-spinal nervous sys¬ 
tem ; 6, cavity of nose; e, cav- Fio. 330. —Transverse Section of Human Body 
ity of mouth; d, alimentary (theoretical): a, cerebro-spinal nervous axis 
canal; e, chain of sympathet- contained in neural tube; e, chain of sympa- 

ic ganglia; /, heart; g, dia- thetic ganglia; d, alimentary canal; /, heart; 

phragm. h, haemal tube. 

Subclass I. —Ornithodelphia. 

These Mammals have but one outlet for the intestine, 
urinary and reproductive organs, as in Birds. They are 
implacental. There is but one order. 








342 


COMPARATIVE ZOOLOGY. 


1. Monotremata. — This order includes two singular 
forms, the Duck-mole ( Ornithorhynchus ) and Spiny Ant- 
eater (Echidna), both confined to the Australian conti¬ 
nent and New Guinea. The former has a covering of 
fur, a bill like that of a Duck, and webbed feet. The lat¬ 
ter is covered with spines, has a long, toothless snout, like 
the Ant-eater’s, and the feet are not webbed. Both bur- 



Fig. 331.—Ornithorhynchus. 


row, and feed upon Insects. The brain is smooth in the 
Ornithorhynchus, and folded in the Echidna. In both, 
the cerebral hemispheres are loosely united by transverse 
fibres, and do not cover the cerebellum and olfactory 
lobes. 176 

Subclass II.— Dideiphia. 

In these implacental Mammals the uterus is divided 
into two parts. 

2. Marsujpialia are distinguished by the fact that the 
young, always born premature, are transferred by the 
mother to a pouch on the abdomen, where they are at¬ 
tached to the nipples, and the milk is forced into their 
mouths by special muscles. 17 * They have “ marsupial 





VERTEBRATA. 



343 

bones ” projecting from the pelvis, which may serve to 
support the pouch; but as the Monotremes have the same 
bones, but no pouch, they doubtless have some other func¬ 
tion. These bones are peculiar to animals having no pla¬ 
centa, namely, to Monotremes and Marsupials. The brains 
of Marsupials resemble those of the Monotremes, except 
that the cerebrum of the Kangaroo covers the olfactory 
lobes. All have the four kinds of teeth, and all are cov¬ 
ered with fur, never with spines or scales. Except the 
Opossums of America, all are restricted to Australia and 


Fig. 332.—Virginian Opossum (Didelphys Virginiana). 


adjacent islands. The Marsupials are almost the only 
Mammals of Australia, a few species of Rodents and Bats 
being the only placental Mammals. The Marsupials have 
here developed into forms corresponding in their habits 
to the orders of placental Mammals in the rest of the 
world. The Kangaroos take the place of the large her¬ 
bivores— the Ungulates. The Thylacinus and Dasyurus 
are the marsupial carnivora. Other forms are squirrel¬ 
like in shape and habits, and still others are insectivorous. 


344 


COMPARATIVE ZOOLOGY. 


Subclass III. —Monodelphia or Placental Mammals. 

In these Mammals the young are connected with the 
mother by means of a vascular structure, the placenta, by 
which they are nourished. They are born in a relatively 
perfect condition. 

3. Edentata .—This strange order contains very diverse 
forms, as the leaf-eating Sloths and the insectivorous Ant- 
eaters and Armadillos of South America, and the Pango¬ 
lin and Orycteropus of the Old World. The gigantic fos- 



rieiai; o, Buperoccipuai; 2, occipital condyles; 

28, tympanic; 73, lachrymal; 32, lower mandi- tile Armadillos and Pail- 
ble. Teeth wanting. .. 


golins, with an armor of 


plates or scales. The Ant-eaters and Pangolins are strict¬ 
ly edentate, or toothless; the rest have molars, wanting, 
however, enamel and roots. In general, it may be said 
that the order includes all quadrupeds having separate, 
clawed toes and no incisors. The Sloths are arboreal; the 



Fig. 334— Armadillo (Dasypus). 



YERTEBRATA. 




345 

others burrow. The brain is generally smooth ; but that 
of the Ant-eater is convoluted, and has a large corpus cal¬ 
losum ; but in all the cerebellum and part of the olfac¬ 
tory lobes are exposed. 

4. Rodentia , or Gnawers, are characterized by two long, 
curved incisors in each jaw, enameled in front, and per¬ 
petually growing; they are specially formed for nibbling. 

15 n 


Fig. 335.—Skull of a Rodent ( Capybara): 22, premaxillary ; 21, maxillary; 26, mo¬ 
lar ; 27, squamosal; 73, lachrymal; 15, nasal; 11, frontal; 4, occipital processes, 
unusually developed; i , incisors; a, angle of lower jaw. 

Separated from them by a wide space (for canines are 
wanting), are the flat molars, admirably fitted for grind¬ 
ing. The lower jaw has longitudinal condyles, which 
work freely backward and forward in longitudinal fur¬ 
rows. Nearly all have clavicles; and the toes are clawed. 
The cerebrum is nearly or quite smooth, and covers but a 
small part of the cerebellum. All are vegetarian. 


Fig. 336.—Incisor Teeth of the Ilare. 









346 


COMPARATIVE ZOOLOGY. 


More than one half of all known Mammals are Rodents. 
They range from the equator to the poles, over every con¬ 
tinent, over mountains and plains, deserts and woods. The 



more important representatives are the Porcupines, Capy- 
baras, Guinea-pigs, Hares, Mice, Rats, Squirrels, and Bea¬ 
vers. The Capybara and Beaver are the giants of the 
race. 

5. Insectivora are diminutive, insect-eating animals, 
some, as the Shrew, being the smallest of Mammals. 


They have small, smooth brains, 
which, as in the preceding orders, 
leave uncovered the cerebellum 
and olfactory lobes. The molar 
teeth bristle with sharp, pointed 
cusps, and are associated with ca¬ 
nines and incisors. They have a 



Fig. 83S.— Shrew Mouse (tiorex). 


long muzzle, short legs, and clavicles. The feet are formed 
for walking or grasping, and are plantigrade, five-toed, and 
clawed. The Shrew, Hedgehog, and Mole are examples. 

6. Cheiroptera , or Bats, repeat the chief characters of 
the Insectivores; but some (as the Flying-fox) are fruit- 
eaters, and have corresponding modifications of the teeth. 
They are distinguished by their very long fore-limbs, 




VERTEBRATA. 


347 


which are adapted for flight, the fingers being immense¬ 
ly lengthened, and united by a membranous web. The 
toes, and one or two of the fingers, are armed with hooked 



Fig. 339—Bat ( Vespertilio). 


nails. The clavicles are remarkably long, and the ster¬ 
num is of great strength ; but the whole skeleton is ex¬ 
tremely light, though not filled with air, as in Birds. The 
eyes are small, the ears large, and the sense of touch is 
very acute. The favorite attitude of a Bat when at rest 
is that of suspension by the claws, with head downward. 
They are all nocturnal. 



Fie. 340.—Skeleton of a Bat. 










348 


COMPARATIVE ZOOLOGY. 


7. Cetacea or Whales, have the form and life of Fishes, 
yet they possess a higher organization than the preceding 
orders. They have a broad brain, with many and deep 
foldings; the foramen magnum of the skull is entirely 
posterior; the whole head is disproportionately large, and 
the jaws greatly prolonged. The body is covered with a 
thick, smooth skin, with a layer of fat (“ blubber”) under- 



Fig. 341.—Outline of the Sperm-whale ( Physeter ): a, blow-hole ; 6, the case contain¬ 
ing spermaceti; c, junk; d, bunch of the neck—between it and the corner of the 
mouth is the eye; k, hump; i, ridge; k, the small; /, tail, or flukes. Between 
the dotted lines are the spiral strips of blubber. Maximum length, sixty feet. 
South Atlantic. 

neath; there are no clavicles; the hind-limbs are want¬ 
ing, and the front pair changed to paddles; the tail ex¬ 
pands into a powerful, horizontal fin; neck and external 
ears are wanting; the eyes small, with only two lids; the 
nostrils (“blow-holes”)—double in the Whale, single in 
the Porpoise—are on the top of the head. All are carniv¬ 
orous, and essentially marine, a few Dolphins only be¬ 
ing found in the great rivers. In the Whalebone Whales, 
the teeth are absorbed, and disappear before birth, and 
their place is supplied by horny “ baleen ” plates. “ The 
Whale feeds by putting this gigantic strainer into opera¬ 
tion, as it swims through the shoals of minute Mollusks, 
Crustaceans, and Fishes, which are constantly found at the 
surface of the sea. Opening its capacious mouth, and al¬ 
lowing the sea-water, with its multitudinous tenants, to fill 
the oral cavity, the Whale shuts the lower jaw upon the 
baleen plates, and, straining out the water through them, 
swallows the prey stranded upon its vast tongue.” In the 


VERTEBRATA. 


349 



Fig. 342.—Greenland Whale (Balcenct mysticetus). North Atlantic. 


other Cetaceans teeth are developed, especially in Dol¬ 
phins and Porpoises; but the Sperm Whale has them only 
in the lower jaw, and the Narwhal can show but a single 
tusk. The Dolphins are the only Mammals having no 
organ of smell. 

8. Sirenia resemble the Cetaceans in shape, but are close¬ 
ly allied to the hoofed animals in organization. They 
have the limbs of the Whales, and are aquatic; but they 
are herbivorous, and frequent great rivers and estuaries. 
They have two sets of teeth, the Cetaceans having but 








350 


COMPARATIVE ZOOLOGY. 



Fig. 343 _ Troop of Dolphins, with Manatee in the distance. 


one. They have a narrow brain; bristles scantily cover¬ 
ing the body; and nostrils placed on the snout, which is 
large and fleshy. The living representatives are the Ma¬ 
natee, of both sides of the tropical Atlantic Ocean, and the 
Dugong, of the East Indies. 

9. Proboscidia. — This race of giants, now nearly ex¬ 
tinct, is characterized by two upper incisors in the form of 
tusks, mainly composed of dentine (ivory). In the extinct 
Dinotherium the tusks projected from the lower jaw; and 
in the Mastodon, from both jaws. Canines are wanting. 
The molars are few and large, with transverse ridges (Ele¬ 
phant) or tubercles (Mastodon). The cerebrum is large 
and convoluted, but does not cover the cerebellum. The 
skull is enormous, the size arising in great measure from 
the development of air-cavities between the inner and 
outer plates. The nose is prolonged into a flexible trunk, 
which is a strong and delicate organ of prehension. There 
are four massive limbs, each with five toes incased in 


VERTEBRATA. 


351 


broad, shallow hoofs, and also with a thick, tegumentary 
pad. The knee is below and free from the body, as in 
Monkeys and Men. Clavicles are wanting. The body of 
the Elephant is nearly naked; but the Mammoth, an ex¬ 
tinct species, had a covering of long woolly hair. Ele¬ 
phants live in large herds, and subsist on foliage and grass. 
There are but two living species: the Asiatic, with long 
head, concave forehead, small ears, and short tusks; and 
the African, with round head, convex forehead, large ears, 
and long tusks. 177 

10. Ungulata , or Hoofed Quadrupeds.—This large or¬ 
der, comprehending many animals most useful to Man, is 
distinguished by four well-developed limbs, each furnished 
with not more than four complete toes, and each toe in¬ 
cased in a hoof. The leg, therefore, has no prehensile 
power; it is only for support and locomotion. Clavicles 
are wanting; and the radius and ulna are so united as to 
prevent rotation. There are always two sets of teeth, i. e. 9 
milk-teeth are succeeded by a permanent set. The grind¬ 
ers have broad crowns. As a rule, all are herbivorous. 
The brain is always convoluted, but the cerebellum is 
largely uncovered. 

Ungulates are divided into the odd and even toed. a. 
The Odd-toed , as the three-toed Rhinoceros and Tapir, 178 
and the one-toed Horse. 179 The first is distinguished by 
its very thick skin, the absence of canines, and one or two 
horns on the nose. The Tapir has the four kinds of teeth, 
and a short proboscis. The dental formula of the Horse 


is— 


c 1 ~ 1 1 vm 3 ~ 3 , m 3 ~_ — 40. 

1 — l’ ^ 3 — 3 3 — 3 


The canines are often wanting in the mare. The Horse 
walks on the third finger and toe. The metacarpals and 
metatarsals are greatly elongated, so that the wrist and 
heel are raised to the middle of the leg. b. The Even-toed 



352 COMPARATIVE ZOOLOGY. 

Ungulates — Hog, Hippopotamus, and Ruminants have 
two or four toes. The Hog and Hippopotamus have the 


four kinds of teeth, and, in the wild state, are vegetarian. 
The Ruminants have two toes on each foot, enveloped in 
hoofs which face each other by a flat side, so that they ap¬ 
pear to be a single hoof split or “ cloven.” Usually there 
are also two supplementary hoofs behind, but they do not 
ordinarily touch the ground. All chew the cud, and have 
a complicated stomach. They have incisors in the lower 
jaw only, and these are apparently eight; but the two 
outer ones are canines. 180 The molars are flat, typical 
grinders. The dental formula of the Ox is— 

i °~° , c °~° , pm 3 ~~_ 3 , m 3 — 3 = 32 . 

With few exceptions, as the Camel, all Ruminants have 
horns, which are always in pairs. Those of the Deer are 
solid, bony, and deciduous; those of the Giraffe and An- 


Fig. 344.—ludiau Rhinoceros (R. unicornis). 









VERTEBRATA. 


353 



Fig. 345.—Stag, or Red Deer (Cervus elaphus). Europe. 



telope are solid, horny, and permanent; in the Goat, 
Sheep, and Ox they are hollow, horny,- and permanent. 

11. Carnivora , or Beasts of Prey, may be recognized by 
their four long, curved, acute, canine teeth, the gap be¬ 
tween the incisors and canines in the upper jaw for the 
reception of the low¬ 
er canine, and molars 
graduating from a tu- 
berculate to a trench¬ 
ant form, in propor¬ 
tion as the diet de¬ 
viates from a miscel¬ 
laneous kind to one 
strictly of flesh. The 
incisors, except in the 

PinnigradeS, number Fig. 346.—Raccoon (Procyon lotor). United States. 


23 


354 


COMPARATIVE ZOOLOGY. 


six in each jaw. There are always two sets. The 
skull is comparatively small, the jaws are shorter and 



Fig. 347.—Wolf (Lupus occidentalis). United States. 



Fig. 34S.—Ermine-weasel (Putorius Noveboracensis). 
United States. 



Fig. 349 —lied Fox (Vulpes fulvus ). United States. 

is covered with abundant hair. 


deeper than in Un¬ 
gulates, and there 
are numerous bony 
ridges on the in¬ 
side and outside 
of the cranium— 
the high occipital 
crest being special¬ 
ly characteristic. 
The cerebral hem¬ 
ispheres are joined 
by a large corpus 
callosum, but the 
cerebellum is nev¬ 
er completely cov¬ 
ered. Both pairs 
of limbs are well 
developed, the 
front being pre¬ 
hensile; but the 
clavicles are rudi¬ 
mentary. The hu¬ 
merus and femur 
are mainly en¬ 
closed in the body. 
The digits, never 
less than four, al¬ 
ways have sharp 
and pointed 
claws. 181 The body 


Carnivores are divided according to the modifications 
ot the limbs: a. Pmnigrades, having short feet expanded 



VERTEBRATA. 


355 


into webbed paddles for swimming, the hinder ones being 
bound in with the skin of the tail. Such are the Seals, 
Walrus, and Eared Seals, or Sea-lions, b. Plantigrades , in 
which the whole, or nearly the whole, of the hind-foot 
forms a sole, and rests on the ground. The claws are not 
retractile; the ears are small, and tail short. Bears, Bad¬ 
gers, and Baccoons are well-known examples, e. Digiti- 
grades keep the heel raised above the ground, walking on 
the toes. The majority have long tails. Such are the 
Weasels, Otters, Civets, Hyenas, Foxes, Jackals, Wolves, 
Dogs, Cats, Panthers, Leopards, Tigers, and Lions. The 



Fig. 350.—Southern Sea-lion (Otaria jubata). Antarctic Ocean. 


last five differ from* all others in having retractile claws, 
and the radius rotating freely on the ulna. The Cats 
have thirty teeth; the Dogs, forty-two, or twelve more 
molars. In the former, the tongue is prickly; in the 
latter, smooth. 

12. Prosimii or Lemurs. These singular mammals, 
sometimes included in the next order, have affinities with 
Kodents, Insectivora, and Primates. They are covered 
with 6oft fur, have usually a long tail, pointed ears, fox¬ 
like muzzle, and curved nostrils. They walk on all fours, 
and the thumb and great toe are generally opposable to 
the digits. The second toe has a long, pointed claw in- 




356 


COMPARATIVE ZOOLOGY. 


stead of a nail. The cerebrum is relatively small, and 
flattened, and does not cover the cerebellum and olfactory 

lobes. 182 They are found 
mainly in Madagascar. 

13. Primates , the head 
of the kingdom, are char¬ 
acterized by the posses¬ 
sion of two hands and 
two feet. The thigh is 
free from the body, and 
all the digits are fur¬ 
nished with nails,the first 

Pig. 351.—Lemur (L. ruber). Madagascar. on the foot enlarged to a 

“great toe.” Throughout the order, the hand is eminently 
or wholly prehensile, and the foot, however prehensile it 
may be, is always locomotive. 193 The clavicles are perfect. 
The eyes are situated in a complete bony cavity, and 
look forward. There are two sets of teeth, all enamelled ; 
and the incisors number four in each jaw. They are 
divided into Monkeys and Apes, and Man. 

The Monkeys of tropical America have, generally,, a 
long, prehensile tail; the nostrils are placed far apart, 
so that the nose is wide and flat; the thumbs and great 
toes are fitted for grasping, but are not opposable to the 
other digits; and they have four molars more than the 
Apes or Man —that is, thirty-six teeth in all. In the 
Apes of the Old World the tail is never prehensile. and 
is sometimes wanting; the nostrils are close together; 
both thumbs and great toes are opposable; and the teeth, 
though numbering the same as Man’s, are uneven (the 
incisors being prominent, and the canines large), and the 
series is interrupted by a gap on one side or other of 
the canines. Their average size is much greater than 
that of the Monkeys, and they are not so strictly arboreal. 
In both Monkeys and Apes, the cerebrum covers the cere- 



VERTEBRATA, 


357 



Tig. 352.—White-throated Sapajou ( Cebus hypolencus). Central America. 

bellum. 184 While in the Monkeys the skull is rounded 
and smooth, that of the Apes, especially those coming 
nearest to Man—the anthropoid, or long-armed, Apes, as 
Gorilla, Chimpanzee, Orang, and Gibbon—is characterized 
by strong crests. Monkeys take a horizontal position; 

but the Apes assume a semi- 
erect attitude, the legs being 
shorter than the arms. In 


Fro, 353.—Skull of Orang-utan (Simia Fig. 354 .—Skull of Chimpanzee ( Troglo • 

satyr us). dytes Niger). 









358 COMPARATIVE ZOOLOGY. 

all the Primates but Man, the body is clothed with hair, 
which is generally longest on the back. Several Mon¬ 
keys and Apes have a beard, as the Howler and Orang. 



Fig. 355.—Female Oraug-utan (from photograph). Borneo. 


The Orang is the least human of all the anthropoid 



Fig. 356.—Skeletons of Man, Chimpanzee, and Orang. 











VERTEBRATA. 


359 


Apes as regards the skeleton, but comes nearest to Man 
in the form of the brain. The Chimpanzee approaches 
Man more closely in the character of its cranium and 
teeth, and the proportional size of the arms. The Gorilla 
is most Man-like in bulk (sometimes reaching the height 
of five feet six inches), in the proportions of the leg to 
the body and of the foot to the hand, in the size of the 
heel, the form of the pelvis and shoulder-blade, and vol¬ 
ume of brain. 1SB 

Man differs from the Apes in being an erect biped. 
In him, the vertebrate type, which began in the horizon¬ 
tal Fish, finally became vertical. No other animal habit¬ 
ually stands erect; in no other are the fore-limbs used 
exclusively for head - purposes, and the hind pair solely 
for locomotion. 

His limbs are naturally parallel to the axis of his body, 
not perpendicular. They have a near equality of length, 
but the arms are always somewhat shorter than the legs. 
In all the great Apes the arms reach below the knee, and 
the legs of the Chimpanzee and Gorilla are relatively 
shorter than Man’s. 

Man only has a finished hand, most perfect as an organ 
of touch, and most versatile. Both hand and foot are 
relatively shorter than in the Apes. The foot is planti- 



360 


COMPARATIVE ZOOLOGY. 


grade; the leg bears vertically upon it; the heel and 
great toe are longer than in other Primates; and the 
great toe is not opposable, but is used only as a fulcrum 
in locomotion. The Gorilla has both an inferior hand 
and inferior foot. The hand is clumsier, and with a 
shorter thumb than Man’s; and the foot is prehensile, 
and is not applied flat to the ground. 186 

The scapular and pelvic bones are extremely broad, 
and the neck of the femur remarkably long. Man is 
also singular in the double curve of the spine: the Ba¬ 
boon comes nearest to Man in this respect. 

The human skull has a smooth, rounded outline, ele¬ 
vated in front, and devoid of crests. The cranium great¬ 
ly predominates over the face, being four to one; 187 and 
no other animal (except the Siamang Gibbon) has a chin. 

Man stands alone in the peculiarity of his dentition: 
his teeth are vertical, of nearly uniform height, and close 
together. In every other animal the incisors and canines 
are more or less inclined, the canines project, and there 
are vacant spaces. 188 

Man has a longer lobule to his ear than any Ape, and 
no muzzle. The bridge of his nose is decidedly convex; 
in the Apes generally it is flat. 

Man has been called the only naked terrestrial Mam¬ 
mal. His hair is most abundant on the scalp; never on 
the back, as in the Apes. 

Man has a more pliable constitution than the Apes, as 
shown by his world-wide distribution. The animals near¬ 
est him soon perish when removed from their native places. 

Though Man is excelled by some animals in the acute¬ 
ness of some senses, there is no other animal in which all 
the senses are capable of equal development. He only 
has the power of expressing his thoughts by articulate 
speech, and the power of forming abstract ideas. 

Man differs from the Apes in the absolute size of 


VERTEBRATA. 


361 



Fig. 358.—Australian Savage. 


brain, and in the greater complexity and less symmetrica] 
disposition of its convolutions. The cerebrum is larger 
in proportion to the cerebellum (being as 8£ to 1), and 
the former not only covers the latter, but projects beyond 
it. The brain of the Gorilla scarcely amounts to one 
third in volume or one half in weight of that of Man. 



Yet, so far as cerebral structure goes, Man differs less 
from the Apes than they do from the Monkeys and Le¬ 
murs. The great gulf between Man and the brute is not 
physical, but psychical. 188 




362 


COMPARATIVE ZOOLOGY. 


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Orders . Tentaottlata.—W ith tentacles: Acineta. 

SERIES, METAZOA.—Animals with cellular tissues, true eggs, and blastoderm. 

Subkingdom I. Spongida.—M etazoa, with numerous incurrent openings, one or few excurrent 
orifices, a skeleton, independent cells. 


Order 1. Mtxospongia.— Gelatinous; no skeleton: Halisarca. 

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ARRANGEMENT OF REPRESENTATIVE FORMS. 363 


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ARRANGEMENT OF REPRESENTATIVE FORMS. 


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Order 1. Tetbabbanchiata.— Having four gills, many tentacles, and an external, chambered shell: Nautilus. 

Order 2. Dibbanohiata.— Two gills; naked; ink-bag; \ f lght arms 0cto P m ‘ 

(ten arms: Septa. 


Subkingdom VI. Arthropoda. —Metazoa, with definite number of segments; jointed legs. 

§ 1. Water-breathing. 

Class I. Crustacea. —Having gills and more than eight jointed legs; four antennte. 

Order 1. Cireipedia. —Fixed; shelly covering; feathery arms: Balanus. 

Order 2. Entomostraoa.— Chitinous shell; joints of abdomen and thorax more or less than fourteen: Cyclops. 


x 


366 


COMPARATIVE ZOOLOGY. 




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Subkingdom VII. Tunicata.— Sac-like metazoa, with branchial-sac: Ascidia. 

Subkingdom Vertebrata.— Internal skeleton; notochord or back-bone; nervous cord dorsal and 
separated from body-cavity; circulation complete; limbs not more than four. 

Division I. Acrania, ) No head, brain, heart, or limbs; white-blood corpuscles; numerous ciliated gill-slits: 


ARRANGEMENT OF REPRESENTATIVE FORMS. 


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develop through tadpole state; two occipital condyles; heart of three cavities; skin soft. 

_ , . __ _ , ( gills permanent: Menobranchus. 

Order 1. Ukodela.— 1 Tailed ; < ... f „ , . 

( gills temporary: Salamandra. 

Order 2. Lahyrintiiodontia _Extinct; bony scales, and complex teeth. 

Order 3. C^oii.ia.—S nake-like; no limbs: Ccecilia. 

m ... A l no teeth: Bufo. 

Order 4. A»o 0 aA.-Tailless; gills temporary; j upper ^ only: Rana 


Subkingdom Vertebeata, Division Craniota — Continued. 

Province II. Sauropsida.—Craniota with amnion and allantois; no gills; one occipital condyle; epidermal 

scales or feathers. 




368 


COMPARATIVE ZOOLOGY. 


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Subkingdom V ertebrata— Continued . 
Province III. Mammalia— Continued. 


370 


COMPARATIVE ZOOLOGY. 


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THE DISTRIBUTION - OF ANIMALS. 


371 


CHAPTER XXIII. 

THE DISTRIBUTION OF ANIMALS. 

Life is everywhere. In the air above, the earth be¬ 
neath, and the waters under the earth, we are surrounded 
with life. Nature lives: every pore is bursting with life; 
every death is only a new birth, every grave a cradle. 
The air swarms with Birds, Insects, and invisible animal¬ 
cules. The waters are peopled with innumerable forms, 
from the Protozoan, millions of which would not weigh a 
grain, to the Whale, so large that it seems an island as it 
sleeps upon the waves. The bed of the sea is alive with 
Crabs, Shells, Polyps, Star-fishes, and Foraminifera. Life 
everywhere—on the earth, in the earth, crawling, creep¬ 
ing, burrowing, boring, leaping, running. 

Nor does the vast procession end here. The earth we 
tread is largely formed of the debris of life. The quarry 
of limestone, the flints which struck the fire of the old 
Revolutionary muskets, are the remains of countless skele¬ 
tons. The major part of the Alps, the Rocky Mountains, 
and the chalk cliffs of England are the monumental rel¬ 
ics of by-gone generations. From the ruins of this living 
architecture we build our Parthenons and Pyramids, our 
St. Peters and Louvres. So generation follows generation. 
But we have not yet exhausted the survey. Life cradles 
within life. The bodies of animals are little worlds hav¬ 
ing their own fauna and flora. In the fluids and tissues, 
in the eye, liver, stomach, brain, and muscles, parasites are 
found; and these parasites often have their parasites liv¬ 
ing on them. 


372 


COMPARATIVE ZOOLOGY. 


“Great fleas have little fleas and smaller fleas to bite ’em; 

And these again have other fleas, and so ad infinitum .” 

Thus the ocean of life is inexhaustible. It spreads in 
every direction, into time past and present, flowing every¬ 
where, eagerly surging into every nook and corner of cre¬ 
ation. On the mountain-top, in the abysses of the Atlan¬ 
tic, in the deepest crevice of the earth’s crust, we find 
traces of animal life. Nature is prodigal of space, but 
economical in tilling it . 190 

Animals are distributed over the globe according to 
definite laws, and with remarkable regularity. 

Each of the three great provinces, Earth, Air, and Wa¬ 
ter, as also every continent, contains representatives of all 
the classes; but the various classes are unequally repre¬ 
sented. Every great climatal region contains some species 
not found elsewhere, to the exclusion of some other forms. 
Every grand division of the globe, whether of land or 
sea, each zone of climate and altitude, has its own fauna. 
And, in spite of the many causes tending to disperse ani¬ 
mals beyond their natural limits, each country preserves 
its peculiar zoological physiognomy. 

The space occupied by the different groups of animals 
is often inversely as the size of the individuals. Compare 
the Coral and Elephant. 

The fauna now occupying a separate area is closely al¬ 
lied to the fauna which existed in former geologic times. 
Thus, Australia has always been the home of Marsupials, 
and South America of Edentates. 

It is a general rule that groups of distinct species are 
circumscribed within definite, and often narrow, limits. 
Man is the only cosmopolitan; yet even he comprises sew 
eral marked races, whose distribution corresponds with the 
great zoological regions. The natives of Australia are as 
grotesque as the animals. Certain brutes likewise have a 
great range: thus, the Puma ranges from Canada to Pata- 


THE DISTRIBUTION OF ANIMALS. 373 

gonia; the Musk - rat, from the Arctic Ocean to Florida; 
the Ermine, from Behring’s Straits to the Himalayas; and 
the Hippopotamus, from the Nile and Niger to the Orange 
River . 191 

Frequently, species of the same genus, living side by 
side, are widely different, while there is a close resem¬ 
blance between forms which are antipodes. The Mud-eel 
of South Carolina and Menobranchus of the Northern 
States have their relatives in Japan and Austria. The 
American Tapir has its mate in Sumatra; the Llama is 
related to the Camel, and the Opossum to the Kangaroo. 

The chief causes modifying distribution are tempera¬ 
ture, topography, ocean and wind currents, humidity and 
light. To these may be added the fact that animals are 
ever intruding on each other’s spheres of existence. High 
mountain-ranges, wide deserts, and cold currents in the 
ocean are impassable barriers to the migration of most 
species. Thus, river-fish on opposite sides of the Andes 
differ widely, and the cold Peruvian current prevents the 
growth of coral at the Galapagos Islands. So a broad 
river, like the Amazons, or a deep, narrow channel in the 
sea, is an effectual barrier to some tribes. Thus, Borneo 
belongs to the Indian region, while Celebes, though but a 
few miles distant, is Australian in its life. The faunse of 
North America, on the east coast, west coast, and the open 
plains between, are very different. 

Animals dwelling at high elevations resemble those of 
colder latitudes. The same species of Insects are found 
on Mount Washington, and in Labrador and Greenland. 

The range does not depend upon the powers of loco¬ 
motion. The Oyster extends from Halifax to Charles¬ 
ton, and the Snapping - turtle from Canada to the equa¬ 
tor ; while many Quadrupeds and Birds have narrow hab¬ 
itats. 

The distribution of any group is qualified by the nature 


374 COMPARATIVE ZOOLOGY. 

of the food. Carnivores have a wider range than herbi¬ 
vores. 

Life diminishes as we depart from the equator north 
or south, and likewise as we descend or ascend from the 
level of the sea. 

The zones of geography have been divided by zoolo¬ 
gists into narrower provinces. Five vertical regions in 
the sea have been recognized: the Littoral, extending be¬ 
tween tide-marks; the Laminarian, from low water to 
fifteen fathoms; the Coralline, from fifteen to twenty 
fathoms; the deep-sea Coral, from fifty to one hundred 
fathoms; and the Bathybian, from one hundred fathoms 
down; but since life has been found to extend to great 
depths in the ocean—as great as three thousand fathoms 
—these divisions are of little importance. Every marine 
species has its own limits of depth. It would be quite as 
difficult, said Agassiz, for a Fish or a Mollusk to cross 
from the coast of Europe to the coast of America as for a 
Beindeer to pass from the arctic to the antarctic regions 
across the torrid zone. Marine animals congregate mainly 
along the coasts of continents and on soundings. The 
meeting-place of two maritime currents of different tem¬ 
peratures, as on the Banks of Newfoundland, favors the 
development of a great diversity of Fishes. 

Every great province of the ocean contains some repre¬ 
sentatives of all the subkingdoms. Deep-sea life is diver¬ 
sified, though comparatively sparse. Examples of all the 
five invertebrate divisions were found in the Bay of Bis¬ 
cay, at the depth of two thousand four hundred and thir¬ 
ty-five fathoms . 192 

Distribution in the sea is influenced by the temperature 
and composition of the water and the character of the 
bottom. The depth acts indirectly by modifying the 
temperature. Northern animals approach nearer to the 
equator in the sea than on the land, on account of cold 


THE DISTRIBUTION OF ANIMALS. 


375 


currents. The heavy aquatic Mammals, as Whales, Wal¬ 
ruses, Seals, and Porpoises, are mainly polar. 

The land consists of the following somewhat distinct 
areas: the Neotropic, comprising South America, the West 
Indies, and most of Mexico; the Nearctic, including the 
rest of America; the Palaearctic, composed of the eastern 
continent north of the Tropic of Cancer, and the Hima¬ 
layas ; the Ethiopian, or Africa south of the Tropic of 
Cancer; the Oriental, or India, the southern part of Chi¬ 
na, the Malay Peninsula, and the islands as far east as 
Java, Borneo, and the Philippine Islands; and the Aus¬ 
tralian, or the eastern half of the Malay Islands and Aus¬ 
tralia. These are Mr. Wallace’s regions. Other writers 
unite the northern parts of both hemispheres into one 
.region, and the Oriental with the Ethiopian regions. 

Life in the polar regions is characterized by great uni¬ 
formity, the species being few in number, though the 
number of individuals is immense. The same animals in¬ 
habit the arctic portions of the three continents; while the 
antarctic ends of the continents, Australia, Cape of Good 
Hope, and Cape Horn, exhibit strong contrasts. Those 
three continental peninsulas are, zoologically, separate 
worlds. In fact, the whole southern hemisphere is pecul¬ 
iar. Its fauna is antique. Australia possesses a strange 
mixture of the old and new. South America, with newer 
Mammals, has older Reptiles; while Africa has a rich 
vertebrate life, with a striking uniformity in its distribu¬ 
tion. Groups, old geologically and now nearly extinct, 
are apt to have a peculiar distribution ; as the Edentata in 
South America, Africa, and India; the Marsupials in Aus¬ 
tralia and America; the Ratitse in South America, Africa, 
Australia, and New Zealand. 

In the tropics, diversity is the law. Life is more varied 
and crowded than elsewhere, and attains its highest devel¬ 
opment. 


376 COMPARATIVE ZOOLOGY. 

The New-world fauna is old-fashioned, and inferior in 
rank and size, compared with that of the eastern con¬ 
tinents. 

As a rule, the more isolated a region the greater the 
variety. Oceanic islands have comparatively few species, 
but a large proportion of endemic or peculiar forms. Ba- 
trachians are absent, and there are no indigenous terrestrial 
Mammals. The productions are related to those of the 
nearest continent. When an island, as Britain, is sepa¬ 
rated from the mainland by a ohallow channel, the mam¬ 
malian life is the same on both sides. 

Protozoans, Coelenterates, and Echinoderms are limited 
to the waters, and nearly all are marine. Sponges are 
mostly obtained from the Grecian Archipelago and Baha¬ 
mas, but species not commercially valuable abound in all 
seas. Coral-reefs abound throughout the Indian Ocean 
and Polynesia, east coast of Africa, Bed Sea, and Persian 
Gulf, West Indies, and around Elorida; and Corals which 
do not form reefs are much more widely distributed, be¬ 
ing found as far north as Long Island Sound and Eng¬ 
land. Crinoids have been found, usually in deep sea, in 
very widely separated parts of the world—off the coast of 
Norway, Scotland, and Portugal, and near the East and 
West Indies. The other Echinoderms abound in almost 
every sea: the Star-fishes chiefly along the shore, the Sea- 
urchins in the Laminarian zone, and the Sea-slugs around 
coral-reefs. Worms are found in all parts of the world, 
in sea, fresh water, and earth. They are most plentiful 
in the muddy or sandy bottoms of shallow seas. Living 
Brachiopods, though few in number, occur in tropical, 
temperate, and arctic seas, and from the shore to great 
depths. Polyzoa have both salt and fresh water forms, 
and Annelids include land forms, as the Earth-worm and 
some Leeches. 

Mollusks have a world-wide distribution over land and 


THE DISTRIBUTION OF ANIMALS. 377 

sea. The land forms are restricted by climate and food, 
the marine by shallows or depths, by cold currents, by 
a sandy, gravelly, or mud bottom. The Bivalves are also 
found on every coast and in every climate, as well as in 
rivers and lakes, but do not flourish at the depth of much 
more than two hundred fathoms. The fresh-water Mus¬ 
sels are more numerous in the United States than in 
Europe, and west of the Alleghanies than east. The sea- 
sliells along the Pacific coast of America are unlike those 
of the Atlantic, and are arranged in five distinct groups: 
Aleutian, Californian, Panamic, Peruvian, and Magel¬ 
lanic. On the Atlantic coast, Cape Cod and Cape Hatte- 
ras separate distinct provinces. Of land Snails, Helix has 
an almost universal range, but is characteristic of North 
America, as Bulimus is of South America, and Achatina 
of Africa. The Old World and America have no species 
in common, except a few in the extreme north. 

The limits of Insects are determined by temperature 
and vegetation, by oceans and mountains. There is an 
insect-fauna for each continent, and zone, and altitude. 
The Insects near the snow-line on the sides of mountains 
in the temperate region are similar to those in polar lands. 
The Insects on our Pacific slope resemble those of Europe, 
while those near the Atlantic coast are more like those of 
Asia. Not half a dozen Insects live in the sea. 

The distribution of Fishes is bounded by narrower lim¬ 
its than that of other animals. A few tribes may be called 
cosmopolitan, as the Sharks and Herrings; but the species 
are local. Size does not appear to bear any relation to 
latitude. The marine forms are three times as numerous 
as the fresh-water. The migratory Fishes of the northern 
hemisphere pass to a more southern region in the spring, 
while Birds migrate in the autumn. 

Living Beptiles form but a fragment of the immense 
number which prevailed in the Middle Ages of Geology. 


378 


COMPARATIVE ZOOLOGY. 


Being less under the influence of Man, they have not been 
forced from their original habitats. None are arctic. 
America is the most favored spot for Frogs and Salaman¬ 
ders, and India for Snakes. Australia has no Batrachians, 
and two thirds of its Snakes are venomous. In the United 



Fig. 361.—Zones of Animal Life. 


States, only twenty-two out of one hundred and seventy- 
six are venomous. Frogs, Snakes, and Lizards occur at 
elevations of over fifteen thousand feet. Crocodiles, and 
most Lizards and Turtles, are tropical. 

Swimming Birds, which constitute about one fourteenth 
of the entire class, form one half of the whole number in 

















THE DISTRIBUTION OF ANIMALS. 


379 


Greenland. As we approach the tropics, the variety and 
number of land Birds increase. Those of the torrid zone 
are noted for their brilliant plumage, and the temperate 
forms for their more sober hues, but sweeter voices. In¬ 
dia and South America are the richest regions. Hum- 
mers, Tanagers, Orioles, and Toucans are restricted to the 
Hew World. Parrots are found in every continent ex¬ 
cept Europe ; and Woodpeckers occur everywhere, save in 
Australia. 

The vast majority of Mammals are terrestrial; but Ce¬ 
taceans and Seals belong to the sea, Otters and Beavers de¬ 
light in lakes and rivers, and Moles are subterranean. As 
of Birds, the aquatic species abound in the polar regions. 
Marsupials inhabit two widely separated areas — America 
and Australia. In the latter continent they constitute 
two thirds of the fauna, while all placental Mammals, ex¬ 
cept Bats and a few Rats and Squirrels, are wanting. 
Excepting a few species in South Africa and South Asia, 
Edentates are confined to tropical South America. The 
equine family is indigenous to South and East Africa and 
Southern Asia. In Horth America, Rodents form about 
one half the number of Mammals; there are but three 
species in Madagascar. Ruminants are sparingly repre¬ 
sented in America. Carnivores flourish in every zone 
and continent. The prehensile-tailed Monkeys are strict¬ 
ly South American ; while the anthropoid Apes belong 
to the west coast of Africa, and to Borneo and Sumatra. 
Both Monkeys and Apes are most abundant near the equa¬ 
tor ; in fact, their range is limited by the distribution of 
palms. 





* 











NOTES. 


1 The complete and elaborate natural history of a single species or limited 
group is called a Monograph , as Darwin’s “Monograph of the Cirripedia.” 
A Memoir is not so formal or exhaustive, giving mainly original investiga¬ 
tions of a special subject, as Owen’s “ Memoir on the Gorilla.” 

4 Before the time of Linnaeus, the Lady-bug, e. g ., was called “the Cocci- 
nella with red coleopters having seven black spots.” He called it Coccinella 
septem-punctata. 

3 Mandino (1315) and Berenger (1518), of Bologna, and Vesalius, of Brus¬ 
sels (1550), were the first anatomists. Circulation of the blood discovered 
by Harvey, 1616. The lacteals discovered by Aserlus, 1622, and the lym¬ 
phatics by Rudbek, 1650. Willis made the first minute anatomy of the brain 
and nerves, 1664. The red blood-corpuscles were discovered by Leeuwen¬ 
hoek and Malpighi, 1675. Infusoria first observed by Leeuwenhoek, 1675; 
the name given by Muller, 1786. Swammerdam was the founder of Ento¬ 
mology, 1675. Comparative anatomy was first cultivated by Perrault, Pec¬ 
quet, Duverney, and Mery, of the Academy ot Paris, the latter part of the 
seventeenth century. Malpighi, the founder of structural anatomy, was the 
first to demonstrate the structure of the lungs and skin, 1690. About the 
same time, Ray and Willoughby first classified Fishes on structural grounds. 
Foraminifers were seen by Beccarius one hundred and fifty years ago; but 
their true structure was not demonstrated till 1835, by Dujardin. Peyssonel 
published the first elaborate treatise on Corals, 1727. Haller was the first to 
distinguish between contractility and sensibility, 1757. White blood-corpus¬ 
cles discovered by Hewson in 1775. Spallanzani was the first to demonstrate 
the true nature of the digestive process, 1780. Cuvier and Geoffroy, in 1797, 
proposed the first natural classification of animals. Before that, all Inverte¬ 
brates were divided into Insects and Worms. Lamarck was the first to study 
Mollusks, 1800; before him, attention was confined to the shell. He sepa¬ 
rated Spiders from Insects in 1812. The law of correlation enunciated by 
Cuvier, 1826. Yon Baer was the founder of Embryology, establishing the 
doctrine omnia ex ovo , 1827; but the first researches in Reproduction were 
made by Fabricius about 1600, and by Harvey in 1651. Wolff, in the last 
century, was the pioneer in observing the phenomena of Development. Sars 
first observed alternate generation, 1833. Dumeril is considered the father 
of Herpetology, and Owen of Odontology. Schleiden and Schwann pub¬ 
lished their celebrated researches in cell-structure, 1841; but Bichat, who 
died 1802, was the founder of Histology. Protoplasm was discovered by 
Dujardin in 1835, and called Sarcode. 



382 


NOTES. 


4 This twofold division is arbitrary. No essential distinction, founded on 
the nature of the elements concerned, or the laws of their combination, can 
be made; and so many so-called organic substances, as urea, ammonia, alco¬ 
hol, tartaric and oxalic acids, alizarine, and glucose, have been prepared by 
inorganic methods, that the boundary-line is daily becoming fainter, and may 
in time vanish altogether. We would here utter our protest against the in¬ 
troduction of any more terms like inorganic, invertebrate, acephalous , etc., 
which express no qualities. 

6 Even the works of nearly all animals proceed in curves. 

6 London Quarterly Review, January, 1869, p. 142. It is true of any great 
primary group of animals, as of a tree, that it is much more easy to define 
the summit than the base. 

7 De Bary on “ MyxomycetceDarwin on “ Carnivorous Plants.” 

8 “There are certain phenomena, even among the higher plants, connected 
with the habits of climbing plants and with the functions of fertilization, 
which it is very difficult to explain without admitting some low form of a 
general harmonizing and regulating function, comparable to such an obscure 
manifestation of reflex nervous action as we have in Sponges and in other 
animals in which a distinct nervous system is absent.”—Prof. Wyville 
Thomson’s Introductory Lecture at Edinburgh. 

9 “ If nature had endowed us with microscopic powers of vision, and the 
integuments of plants had been rendered perfectly transparent to our eyes, 
the vegetable world would present a very different aspect from the apparent 
immobility and repose in which it is now manifested to our senses.”— Hum¬ 
boldt’s Cosmos, i., 341. 

10 See Gray’s “Structural Botany,” p. 350; Rolleston’s “Forms of Ani¬ 
mal Life,” p. 143. 

11 “Life has been called the vital force, and it has been suggested that it 
may be found to belong to the same category as the convertible forces, heat 
and light. Life seems, however, to be more a property of matter in a certain 
state of combination than a force. It does no work, in the ordinary sense.” 
—Prof. Wyville Thomson. 

12 There was a time in our history when a single membrane discharged 
all the functions of life — digesting, respiring, secreting. The separation 
of a heart, lung, stomach, liver, etc., for special duty was an after-considera¬ 
tion. 

13 The vegetable cell has usually two concentric coverings: cell-wall and 
primordial utricle. In animal cells the former is wanting, the membrane 
representing the utricle. As a general fact, animal cells are smaller than 
vegetable cells. 

14 Cells are not the sources of life, as once thought, but are the products 
of protoplasm. “ They are no more the producers of vital phenomena than 
the shells scattered in orderly lines along the sea-beach are the instruments 
by which the gravitation - force of the moon acts upon the ocean. Like 
these, the cells mark only where the vital tides have been and how they 
have acted.”—Prof. Huxley. 

15 Many of the bones of the skull are preceded by membrane—hence called 
membrane-bones. 


NOTES. 


383 

In the heart, the muscular fibres are striated, yet involuntary; but the 
sarcolemma is wanting. 

17 Other names are medullary sheath and white substance of Schwann. 

We may, however, infer that the animal functions are not absolutely 
essential to the vegetative, from the facts that plants digest without mus¬ 
cles or nerves, and that nutrition takes place in the embryo long before the 
nerves have been developed. 

This is not strictly true, for the Elm and Oak, the Trout and Alligator, 
do reach a maximum size. 

20 Scorpions and Spiders properly feed upon the juices of their victims 
after lacerating them with their jaws, but fragments of Insects have been 
found in their stomachs. 

The real tongue forms the floor of the mouth, and is found as a distinct 
part in a few Insects, as the Crickets. 

22 In the Marsipobranchii, it is circMar or oval. 

23 The mouth of the Whale is exceptional, the walls not being dilatable. 
The act of sucking is characteristic of all young Mammals, hence the need 
of lips. 

24 The Ant-eater has two callous ridges in the mouth, against which the 
insects are crushed by the action of the tongue. 

25 The baleen plates do not represent teeth; for in the embryo of the 
Whale we find minute calcareous teeth in both jaws, which never cut the 
gum. The whalebone is a peculiar development of hair in the palate, and 
under the microscope it is seen to be made up of fibres which are hollow 
tubes. 

26 The “ tusks” of the Elephant are prolonged incisors ; those of the Wal¬ 
rus, Wild Boar, and Narwhal are canines. 

27 “I was one day talking with Prof. Owen in the Hunterian Museum, 
when a gentleman approached, with a request to be informed respecting the 
nature of a curious fossil which had been dug up by one of his workmen. 
As he drew the fossil from a small bag, and was about to hand it for exam¬ 
ination, Owen quietly remarked, ‘That is the third molar of the under¬ 
jaw of an extinct species of rhinoceros.’” — Lewes’s Studies in Animal 
Life. 

2S This gap or interspace, so characteristic of the inferior Mammals, is 
called diastema. It is wanting in the extinct Anoplotherium, is hardly per¬ 
ceptible in one of the Lemurs, and is not found in Man. 

29 In the Spermaceti-whale, the teeth are fixed to the gum. 

:0 The Iguana among Reptiles, and Fishes with pavement-teeth, approach 
the Mammals in this respect. 

31 This movement is called peristaltic or vermicular, and characterizes all 
the successive movements of the alimentary canal. 

32 Fishes and Amphibians have no saliva, but a short gullet. Birds are 
aided by a sudden upward jerk of the head. 

33 Fishes and Reptiles have no pharynx proper, the nostrils and glottis 
opening into the mouth. 

34 This movement of the pharynx and oesophagus is wholly involuntary. 
Liquids are swallowed in exactly the same way as solids. 


384 


NOTES. 


85 The few animals in which the digestive cavity is wanting are called 
agastric , and agree in having a very simple structure. Such are some Ento- 
zoa (as Tape-worm) and unicellular Protozoa (as Gregarina). They absorb 
the juices, already prepared, by the physical process of endosmose. There 
are other minute organisms which seem to be able to extract the necessary 
elements, CHON, from the medium in which they live. 

36 The cavity of a Sponge is perhaps homologous with the digestive cavity, 
but is not functionally such. Each cell lining it does its own digestion, tak¬ 
ing the food from the water circulating in the cavity. 

37 “Nothing is more curious and entertaining than to watch the neatness 
and accuracy with which this process is performed. One may see the rejected 
bits of food passing rapidly along the lines upon which these pedicellarias 
occur in greatest number, as if they were so many little roads for the con¬ 
veying away of the refuse matters; nor do the forks cease from their labor 
till the surface of the animal is completely clean and free from any foreign 
substance.”— Agassiz’s Seaside Studies. 

88 In the larva of the Bee, the anal orifice is wanting. 

38 The length of the canal in Insects is not so indicative of the habits as in 
Mammals. Thus, it is nearly as long and more complicated in the carnivo¬ 
rous Beetles than in the honey-sipping Butterflies. 

40 The object of this is unknown. It does not occur in the Oyster. 

41 In the Nautilus, this is preceded by a capacious crop. 

42 In the Shark, this is impossible, owing to a great number of fringes in 
the gullet hanging down towards the stomach. 

43 At the beginning of the large intestine in the Lizards (and in many Ver¬ 
tebrates above them, especially the vegetarian orders), there is a blind sac, 
called caecum. 

44 The Crocodile is said to swallow stones sometimes, like Birds, to aid 
the gastric mill. 

45 In the crop of the common Fowl, vegetable food is detained sixteen 
hours, or twice as long as animal food. The Dormouse, among Mammals, 
has an approach to a crop. 

46 In Invertebrates, the gizzard, when present, is situated between the crop 
and the true stomach; in Birds, it comes after the stomach. 

47 The Tape-worm has no digestive apparatus, but absorbs the already di¬ 
gested food of its host. This is no exception to the rule. The chemical 
preparation of the food has preceded its absorption. 

48 We find the most abundant saliva in those Mammals that feed on herbs 
and grain, but its action on starch is extremely feeble. 

49 It is probable that the digestive part of the alimentary canal in all 
animals manifests a similar mechanical movement. It is most remark¬ 
able in the gizzard of a fowl, which corresponds to the pyloric end of 
the human stomach. This muscular organ, supplying the want of a mas¬ 
ticatory apparatus in the head, is powerful enough to pulverize not only 
grain, but even pieces of glass and metal. This is done by two hard 
muscles moving obliquely upon each other, aided by gravel purposely swal¬ 
lowed by the bird. The grinding may be heard by means of the stetho¬ 
scope. 


NOTES. 385 

50 Chyle is opaque in carnivores; more or less transparent in all other Ver¬ 
tebrates, as in Birds, since the food does not contain fatty matter. 

51 In Fishes, the villi are few or wanting. In Man, they number about 
10,000 to the square inch. 

32 Except, perhaps, the tendons, ligaments, epidermis, etc. 

53 The phenomenon produced by these properties conjointly, capillary at¬ 
traction and diffusion, is called endosmosis. 

54 The blood is colorless also in the muscular part of Fishes. That of 
Birds is of the deepest red. The coloring matter of the red blood in worms 
is not in the corpuscles, but in the plasma. 

55 Coagulation may be artificially arrested by common salt. Arterial blood 
coagulates more rapidly than venous. The disposition of the red corpuscles 
in chains, or rouleaux , does not occur within the blood-vessels. The cause 
has not been discovered. 

36 The corpuscles of Invertebrates are usually colorless, even when the 
blood is tinged. 

57 Except during the foetal life. The corpuscles of the Camel are non- 
nncleated, as in other Mammals. If the transparent fluid from a boil be 
examined with a microscope, it will be seen to be almost composed of col¬ 
orless corpuscles, showing their use in repairing injuries. 

38 There are no valves in the veins of Fishes, Reptiles, and Whales, and 
few in Birds. 

59 Capillaries are wanting in the epidermis, nails, hair, teeth, and cartilages. 
Hence, the epidermis, for example, when worn out by use, is not removed by 
the blood, like other tissues, but is shed. 

60 A part of the blood, however, in going from the capillaries to the heart, 
is turned aside and made to pass through the liver and kidneys for purifica¬ 
tion. This is called the portal circulation, and exists in all Vertebrates, ex¬ 
cept that in Birds and Mammals it is confined to the liver. 

61 Two in the higher Mammals, three in the lower Mammals, Birds,.and. 
Reptiles. They are called venae, cavce. 

62 Tricuspid in Mammals, triangular in Birds. 

63 The pulse of a Hen is 140; of a Cat, 110 to 120; of a Dog, 90 to 100; 
and of an Ox, 25 to 42. 

64 The bivalve Brachiopods breathe by delicate arms about the mouth, and 
bv the “ mantle.” 

65 The air-bladder, found in most Fishes, is another rudiment of a lung, 
although it is used, not for respiration, but for altering the specific gravity 
of the Fish. In the Gar-pike of our Northern lakes, it very closely resem¬ 
bles a lung, having a cellular structure, a tracheal tube, and a glottis. It is 
here functional. The gills represent lungs only in function; they are totally 
distinct parts of the organism. 

i ee In the human lungs they number 600,000,000, each about of an 
inch in diameter, with an aggregate area of 132 square feet. Ihe thickness 
of the membrane between the blood and the air is 2 ^ 5 ^ of an inch. The 
lungs of Carnivores are more highly developed than those of Herbivores. In 
the Manatee, they are not confined to the thorax, but extend down nearly to 
the tail. 


25 


386 


NOTES. 


67 Crocodiles are the only Reptiles whose nostrils open in the throat behind 
the palate, instead of directly into the mouth-cavity. This enables the Croc¬ 
odile to drown its victim without drowning itself; for, by keeping its snout 
above water, it can breathe while its mouth is wide open. 

68 A rudimentary diaphragm is seen in the Crocodile and Ostrich. 

69 The poison-glands of venomous Serpents and the silk-vessels of Cater¬ 
pillars are considered to be modified salivary glands. Birds, Snakes, and 
Cartilaginous Fishes have no urinary bladder. 

70 Since the weight of a full-grown animal remains nearly uniform, it must 
lose as much as it receives ; that is, the excretions, iucluding the solid resid¬ 
uum ejected from the intestinal canal, equal the food and drink. 

71 Other names for derm are, cutis , corium , enderon , and true skin; and 
for epidermis, cuticle , ecderon, and scarf-skin. The derm is often so inti¬ 
mately blended with the muscles that its existence as a distinct layer is not 
easily made out. Even in Infusoria, we find the tunic double, an outside 
cuticula lined by a soft cortical layer; and in Jelly-fishes, naturalists distin¬ 
guish an ectoderm , endoderm , and mesoderm. 

72 See Fig. 148. Papilla} are scarcely visible in the skin of Reptiles and Birds. 

73 The animal basis of this structure is chitine, a peculiar horn-like substance 
found in the hard parts of all the articulated animals. 

74 The shell is always an epidermal structure, even when apparently internal. 
The horny “pen” of the squid, the “bone” of the Cuttle-fish, and the cal¬ 
careous spot on the back of the Slug are only concealed under a fold of the 
mantle. So the shell of the common Unio, or fresh-water clam, is covered 
with a brownish or greenish membrane, which is the outer layer of the epider¬ 
mis. Where the mantle covers the lips of a shell, as in most of the large sea- 
snails, or where its folds cover the whole exterior, as in the polished Cowry, 
the epidermis is wanting, or covered up by an additional layer. 

75 The pearls of commerce, found in the mantle of some Mollusks, are simi¬ 
lar in structure to the shell; but what is the innermost layer in the shell is 
placed on the outside in the pearl, and is much finer and more compact. The 
pearl is formed around some nucleus, as an organic particle, or grain of sand. 

76 When the centrum is concave on both sides, as in Fishes, it is said to be 
amphicoelous; when concave in front and convex behind, as in Crocodiles, 
it is called procoelous; when concave behind and convex in front, as in the 
neck-vertebrae of the Ox, it is opisthoccelous. In the last two cases, the ver¬ 
tebrae unite by ball-and-socket joints. 

77 Whether the skull represents any definite number of vertebrae is still 
under discussion. We cannot speak of “cranial vertebrae” in the same 
sense as “ cervical vertebrae.” The most that can be said is that in a general 
way the skull is homologous to part of the vertebral column (B). 

78 A few have but one pair, the Whale and Siren wanting the hind pair; 
while some have none at all, as the Snakes and lowest Fishes. In land ani¬ 
mals, the posterior limbs are generally most developed : in aquatic animals, 
the anterior. Dr. Wyman contends that the limbs are tegumentarv organs, 
and attached to the vertebral column in the same sense that the teeth are 
attached to the jaws. Other theories are that they originate from gill-arches 
(Gegenbaur) or that they are remains of a once continuous lateral fin (Thacher). 


NOTES. 


387 


79 The first trace of muscular tissue is found in the stem of Vorticella—an 
Infusorian. In Hydra we find neuro-muscular cells, and the Jelly-fishes 
have muscular tissue. 

80 The muscles of some Invertebrates, as Spiders, are yellow. 

The muscles of the heart and gullet are striped. In the lower animals 
these distinctions of voluntary and involuntary, striated and smooth, solid 
and hollow, muscles can seldom be made. 

The skeleton of the Carrion-crow, for example, weighs, when dry, only 
twenty-three grains. 

The Dragon-fly can outstrip the Swallow; nay, it can do in the air more 
than any bird—it can fly backward and sidelong, to right or left, as well as 
forward, and alter its course on the instant without turning. It makes twen- 
ty-eight beats per second with its wings; while the Bee makes one hundred 
and ninety, and the House-fly three hundred and thirty. The swiftest Kace- 
horse can double the rate of the Salmon. So that Insect, Bird, Quadruped, 
and Fish would be the order according to velocity of movement. 

The theory that Flies adhere by atmospheric pressure is now abandoned. 

85 More precisely, the term brain, or brains, applies only to the cerebrum, 
while the total contents of the cranium are called encephalon. 

86 The exact functions of the cerebrum are not yet clearly understood. 
If we remove it from Fishes, or even Birds, their voluntary movements are 
little atfected; while the Amphioxus, the lowest of Fishes, has no brain at 
all, but its life is regulated by the spinal cord. Such mutilated animals, 
however, make no intelligent efforts. The substance of the cerebrum, as 
also the cerebellum, is insensible, and may be cut away without pain to the 
animal; and when both are thus removed, the animal still retains sensation, 
but not consciousness. 

87 It is very difficult to define sensation, or sensibility. The power is pos¬ 
sessed by animals which have neither nervous system nor consciousness. 
These low manifestations of sensibility are called irritability—the power by 
which an animal is capable of definitely responding to a stimulus from with¬ 
out. The response is not called out by the direct action of the stimulus, but 
is determined mainly by the internal structure and condition of the animal. 

88 Parts destitute of blood-vessels,'as hair, teeth, nails, cartilage, etc., are 
not sensitive. The impressibility of the nerves is proportioned to the activ¬ 
ity of circulation. According to the recent investigations of Dr. Bowditch, 
the channels of motor and sensitive impressions lie in the lateral, and not in 
the anterior and posterior, columns of the spinal cord. 

89 “Tentacles” and “horns” are more or less retractile, while antennae 
are not, but all are hollow. Antennae alone are jointed. 

90 In Man, the soft palate and tonsils also have the power of tasting. 

91 No organ of hearing has been discovered with certainty in the Radiates 
and Spiders. The “ear” of many lower animals is probably an organ for 
perceiving the animal’s position rather than sound—an “equilibrium organ.” 

92 It is wanting in the aquatic Mammals. Crocodiles have the first repre¬ 
sentative of an outsidfe ear in the form of two folds of skin. 

93 This, like the definition of smell and hearing, is loose language. There 
is no such thing as sound till the vibrations strike the tympanum, qor even 


388 


NOTES. 


then, for it is the work of the brain, not of the auditor ) 7 nerve. Sound is 
the sensation produced by the wave-movement of the air. If thus defined 
in terms of sensation, light is nothing; without eyes the world would be 
wrapped in darkness. Some Protozoa have a pigment spot as an eye. 

94 In Invertebrates and aquatic Vertebrates, the crystalline lens is globu¬ 
lar; or, in other words, it is round in short-sighted animals, and flattish i# 
the long-sighted. The lens of the Invertebrate is not exactly the same as 
the lens of the Vertebrate eye, though it performs the same function; it is 
really a part of the cornea. 

95 The Ant has fifty in each eye, the House-fly four thousand, the Dragon¬ 
fly twenty-eight thousand. 

96 The pigment, therefore, while apparently in front of the retina, is really 
behind it, as in Vertebrates. The layer beneath the cornea, serving as an 
“iris,” is wanting in nocturnal Insects, since they need every ray of light. 
The optic nerve alone is insensible to the strongest light. 

97 It should be noticed that this corresponds with another peculiar fact 
already mentioned, that either hemisphere of the brain controls the muscles 
on the opposite side of the body. In Invertebrates, the motor apparatus is 
governed on its own side. 

98 Sharks have eyelids, while Snakes have none. The third eyelid (called 
nictitating membrane) is rudimentary in many Mammals. 

99 An infant would doubtless learn to walk if brought up by a wild beast, 
since it was made to walk. Just as an Infusorium moves its cilia, not be¬ 
cause it has any object, but because it can move them. New-born puppies, 
deprived of brains, have suckled; and decapitated Centipedes run rapidly. 
Such physical instincts exist without mind, and may be termed “blind im¬ 
pulses.” 

100 We say “apparently,” because it may be a fixed habit, first learned by 
experience, transmitted from generation to generation. A duckling may go 
to the water, and a hound may follow game in some sense, as Sir John Her 
schel takes to astronomy, inheriting a taste from his father. Breeders take 
advantage of this power of inheritance. 

101 We may divide the apparently voluntary actions of animals into three 
classes. First, organic , in which consciousness plays no part, and which are 
due wholly to the animal machine. Second, instinctive , in which conscious¬ 
ness may be present, but which are not controlled by intelligence. Third, 
associative, in which the animals act under conscious combination of distinct, 
single ideas, or past impressions. To these we may add rational acts, in 
which the mental process takes place under the laws of thought. 

i °2 “Thus, while the human organism may be likened to a keyed instru¬ 
ment, from which any music it is capable of producing can be called forth at 
the will of the performer, we may compare a Bee, or any other Insect, to a 
barrel-organ, which plays with the greatest exactness a certain number of 
tunes that are set upon it, but can do nothing else.”— Carpenter’s Mental 
Physiology , p. 61. This constancy may be largely due to the uniformity of 
conditions under which Insects live. 

101 We may say, as a rule, that the proportion of instinct and intelligence 
in an animal corresponds to the relative development of the spinal cord and 


NOTES. 


389 


cerebrum. As a rule, also, the addition of the power to reason comes in 
with the addition of a cerebrum, and is proportiohed to its development. 
Between the lowest Vertebrate and Man, therefore, we observe successive 
types of intelligence. Intelligence, however, is not according to the size of 
the brain (else Whales and Elephants would be wisest), but rather to the 
amount of gray matter in it. A honey-comb and an Oriole’s nest are con¬ 
structed with more care and art than the hut of the savage. It is true, this 
is no test of the capability of the animal in any other direction; but when 
they are fashioned to suit circumstances, there is proof of intelligence in one 
direction. 

104 An exception to the general rule that the smaller animals have more 
acute voices. 

105 It is wanting in a few, as the Storks. 

106 The Nightingale and Crow have vocal organs similarly constructed, yet 
one sings and the other croaks. 

107 These cells are detached portions of the parental organisms. Gener¬ 
ally, these two kinds of cells are produced by separate sexes; but in some 
cases, as the Snail, they originate in the same individual. Such an animal, 
in which the two sexes are combined, is called an hermaphrodite. 

108 The eggs of Mammals are of nearly uniform size; those of Birds, 
Insects, and most other animals are proportioned to the size and habits of 
the adult. Thus, the egg of the iEpyornis, the great extinct bird of Mada¬ 
gascar, has the capacity of fifty thousand Humming-birds’ eggs. 

109 As a general rule, when both sexes are of gay and conspicuous colors, 
the nest is such as to conceal the sitting Bird; while, whenever there is a 
striking contrast of colors, the male being gay and the female dull, the nest 
is open. Such as form no nest are many of the Waders, Swimmers, Scratch- 
ers, and Goatsuckers. 

110 This lies at first transversely to the long axis of the egg. As the chick 
develops, it turns upon its side. 

111 The blood appears before the true blood-vessels, in intercellular spaces. 
It is at first colorless, or yellowish. 

112 Exactly as the blood in the capillaries of the lungs is aerated by the 
external air. 

113 Thus, the hollow wing-bone was at first solid, then a marrow-bone, and 
finally a thin-walled pneumatic bone. The solid bones of Penguins are ex¬ 
amples of arrested development. 

114 The thigh-bone ossifies from five centres. The bone eventually unites 
io one piece. 

115 Muscle is mainly fibrine and myosin, while nerve is neurin. 

116 For this reason, Mammals are called viviparous; but, strictly speaking, 
they are as oviparous as Birds. The process of reproduction is the same, 
whether the egg is hatched within the parent or without. The eggs of 
Birds contain whatever is wanted for the development of the embryo, except 
heat, which must come from without. Mammals, having no food-yolk, obtain 
their nutrition from the blood of the parent, and after birth from milk. 

117 The larvae of Butterflies and Moths are called caterpillars; those of 
Beetles, grubs ; those of Flies, maggots; those of Mosquitoes, wigglers. The 


390 


NOTES. 


terms larva , pupa, and imago are relative only; for, while the grub and cat¬ 
erpillar are quite different from the pupa, the bee-state is reached by a very 
gradual change of form, so that it is difficult to say where the pupa ends 
and the imago begins. In fact, a large number of Insects reach maturity 
through an indefinite number of slight changes. The Humble-bee moults at 
least ten times before arriving at the winged state. 

118 Every tissue of the larva disappears before the development of the new 
tissues of the imago is commenced. The organs do not change from one 
into the other, but the new set is developed out of formless matter. The 
pupa of the Moth is protected by a silken cocoon, the spinning of which was 
the last act of the larva; that of the Butterfly is simply enclosed in the dried 
skin of the larva, which is called chrysalis because of its golden spots. The 
pupa of the Honey-bee is called nymph; it is kept in a wax-cell lined with 
silk, spun by the nursing-bee, not by the larva. The time required to pass 
from the egg to the imago varies greatly: the Bee consumes less than twenty 
days, while the Cicada requires seventeen years. 

119 Compare the amount of food required in proportion to the bulk of the 
body, and also with the amount of work done, in youth, manhood, and old age. 

120 Excepting, perhaps, that the new tail of a Lizard is cartilaginous. 

191 The patella, or knee-pan, has no representative in the fore-limb, and. 
strictly, it belongs to the muscular system, rather than to the skeleton. Some 
anatomists contend that the great toe is homologous with the little finger, in¬ 
stead of the thumb. 

i 22 “The structure of the highest plants is more complex than is that of 
the lowest animals; but, for all that, powers are possessed by Jelly-fishes of 
which oaks and cedars are devoid.”— Mivart. 

129 It is, however, true that the number of eggs laid is proportioned to the 
risk in development. 

124 According to Mr. Darwin, the characters which naturalists consider as 
showing true affinity between two or more species are those which have been 
inherited from a common parent; and, in so far, all true classification is gene¬ 
alogical; i. e., it is not a mere grouping of like with like, but it includes like 
descent, the cause of similarity. In the existing state of science, a perfect 
classification is impossible, for it involves a perfect knowledge of all animal 
structure and life’s history. As it is, it is only a provisional attempt to ex¬ 
press the real order of nature, and it comes as near to it as our laws do in 
explaining phenomena. It simply states what we now know about compar¬ 
ative anatomy and physiology. As science grows, its language will become 
more precise and its classification more natural. 

125 The term type is also used to signify that form which presents all the 
characters of the group most completely. Each genus has its typical species, 
each order its typical genus, etc. The word is also applied to the specimen 
on which a new species is founded. A persistent type is one which has con¬ 
tinued with very little change through a great range of time. The family of 
Oysters has existed through many geological ages. 

126 The Ccelenterata and Echinodermata together make up the hadiata y 
the old subkingdom of Cuvier. Echinoderma is probably more correct than 
Echinodermata , but we retain the old orthography. 


NOTES. 


391 


127 Strictly speaking, no individual is independent. Such is the division 
of labor in a hive, that a single Bee, removed from the community, will soon 
die, for its life is bound up with the whole. An individual repeats the type of 
its kingdom, subkingdom, class, order, family, genus, and species, through its 
whole line of descent. 

1 128 These definitions of the various groups are mainly taken from Agassiz. 

They are not practically very useful, as they are not used by working natu¬ 
ralists. The kind and degree of difference entitling a group to a particular 
rank varies greatly with the naturalist, and the part of the Animal Kingdom 
where the group is found. Some families of Insects are separated by gaps 
less than those which divide genera of Mammals. 

129 The Millepore coral, so abundant in the West Indian Sea, is the work 
of Hvdroids. The surface is nearly smooth, with minute punctures. Ge- 
genbauer, Haeckel, and others hold that the Acalephs have no body-cavity 
at all, the internal system of canals being homologous with the intestinal 
cavity of other animals. 

130 This digestive cavity is really homologous to the proboscis of the Jelly¬ 
fish, turned in. It is lined with ectoderm. The “ body-cavity ” is not really 
such, but homologous to the digestive sac of the Hydra. 

131 Among the exceptions are Tubipora , which have eight tentacles and no 
septa, and the extinct Cyathophylla, whose septa are eight or more. 

132 The longer septa (called primary) are the older; the shorter, secondary 
ones, are developed afterwards. As a rule, sclerodermic corals are calcare¬ 
ous, and a section is star-like; the sclerobasic are horny and solid. The 
latter are higher in rank. 

133 Some Star-fishes ( Solaster ) have twelve rays. In all Echinoderms, 
probably, sea-water is freely admitted into the body-cavity around the viscera. 

134 The shell is not strictly external, like the crust of a Lobster, but is 
coated with the soft substance of the animal. 

135 Six hundred pieces have been counted in the shell alone, and twelve 
hundred spines. The feet number about eighteen hundred. They can be 
protruded beyond the longest spines. 

136 The classification of this edition may be compared with that of the for¬ 
mer by the following table, in which the order of the groups is altered to show 
the relation more easily. 


Former Edition. 
Subkingdom. 


III. 

Mollusca. 


IV. 

Articulata. 


Class. 

Class. 


4. Lamellibranchiata. 

Do. 

1. 

5. Gasteropoda. 

Do. 

2. 

6. Cephalopoda. 

3. Tunicata 

Do. 

3. 

2. Brachiopoda. 

Do. 

4. 

1. Polyzoa. 

Do. 

5. 

f 1. Platyhelminthes. 
2. Nematelminthes. 

1. Annelida = -j 

| 3. Kotifera. 

1 6. Annelides. 



2. Crustacea. 

Do. 

1 . 

3. Arachnida. 

Do. 

2. 

4. Myriapoda. 

Do. 

3. 

5. Insecta. 

Do. 

-• 


Present Edition. 

Subkingdom. 

V. 

Mollusca. 

VII. 

Tunicata. 


IV. 

Vermes. 


VI. 

Arthropoda, 






392 


NOTES. 


The two subkingdoms of the earlier edition are thus divided into four. The 
Classes remain the same, except the Annelida. 

137 The most important genera are Terebratula , Rhynchonel la, Discina , 
Lingula , Orthis, Spirifer, and Productus. The first four have representa¬ 
tives in existing seas. Most naturalists now admit their affinity to the 
worms, although some still keep them in the subkingdom Mollusca. 

138 qq iere are some exceptions: the Oyster is unequivalved, and the Pecten 
equilateral. 

139 The chief impressions left on the shell are those made by the muscles— 
the dark spots called “ eyes ” by oyster-men; the pallial line made by the 
margin of the mantle; and the bend in the pallial line, called pallial sinus, 
which exists in those shells having retractile siphons, as the Clam. 

140 The Clam is the highest of Lamellibranchs, and the Oyster one of the 
lowest. The Mya arenaria , or “Soft Clam,” has its shell always open a 
little; while Venus mercenaria , or “ Hard Clam,” keeps its shell closed. 

141 The Slug has no shell to speak of, and the Chiton is covered with eight 
pieces. It may be remembered, as a rule, that all univalve shells in and 
around the United States are Gasteropods, and that all bivalves in our rivers 
and lakes, and along our sea-coasts (save a few Brachiopods), are Lamelli¬ 
branchs. 

142 Hold the shell with the apex up and the mouth towards the observer. 
If the mouth is on his right, the shell is right-handed or dextral, if on his 
left, sinistral. In other words, a right-handed shell is like a right-handed 
screw. 

143 Instead of a strong breathing-tube with a valve, answering for a force- 
pump and propeller, as in the Cuttle-fish, it has only an open gutter made by 
a fold in the mantle, like the siphons of the Gasteropods. The back cham¬ 
bers are filled with nitrogen gas. 

The common Poulpe has two thousand suckers, each a wonderful little air- 
pump, under the control of the animal’s will. 

144 The order of the classes is one of relation rather than of rank. They 
cannot be arranged serially. The Myriapods have a worm-like multiplica¬ 
tion of parts, degrading them, and their nervous system is simpler than that 
of Caterpillars; yet their heads show a close relationship to Insects. The 
Arachnids include some lower forms than Myriapods; on the other hand, 
for their wonderful instincts, Owen places them above the Insects. They are 
closely allied to Crustaceans, and stand more nearly between Crustaceans and 
Insects than between Myriapods and Insects. 

145 Certain Crabs live on dry land, but they manage to keep their gills 
wet. 

146 The student should remember that this threefold division is not equiva¬ 
lent to the like division of a vertebrate body. 

147 Each ring (called somite) is divisible in two arcs, a dorsal and ventral, 
and each arc consists of four pieces. 

148 The four pairs of legs in Arachnids answer to the third pair of maxillae 
and the three pairs of maxillipedes in the Lobster. The great claws of 
Scorpions are the first maxillae of the Lobster, as are the pedipalpi of 
Spiders. 


NOTES. 


393 


149 The antennas are more probably altogether undeveloped, and the jaws 
of the Spider correspond to the mandibles of the Lobster. 

150 Compare the single thread of the Silk-worm and other caterpillars. 

lo1 The common Spider, Epeira, which constructs with almost geometri¬ 
cal precision its net of spirals and radiating threads, will finish one in forty 
minutes, and just as regularly if confined in a perfectly dark place. 

152 These parts do not correspond to the parts so named in human anatomy. 
See also p. 162. 

153 The pupa-case is often ornamented with golden spots in Butterflies; 
hence the common name chrysalis. 

154 In aquatic animals the posterior limbs are the ones aborted or reduced, 
if any; in land animals the fore-limbs are usually sacrificed. 

155 The smallest corpuscles are found in Ruminants; the largest in Am¬ 
phibians with permanent gills. The average size in Birds is double that in 
Man, and about equal to that in the Elephant. Those of Monkeys are a 
trifle smaller than the human. In the embryo they are larger than in the 
adult. Camels only among Mammals have oval disks. 

156 The facial angle becomes of less and less importance as we go away 
from man, and for two reasons. Where the brains do not fill the brain-case 
the angle is obviously of little value, and if the jaws are largely developed the 
angle is reduced, although intelligence may not be altered. 

157 Oblong human skulls, whose diameter from the frontal to the occipital 
greatly exceeds the transverse diameter, are called dolichocephalic; and such 
are usually prognathous , i. e., have projecting jaws, as the negro’s. Round 
skulls, whose extreme length does not exceed the extreme breadth by a 
greater proportion than 100 to 80, are braehycephalic; and such are gener¬ 
ally orthognathous , or straight-jawed. 

158 The classes are variously grouped into the Hcematocrya, or Cold¬ 
blooded, and the Hcematotherma , or Warm-blooded ; into the Branchiata 
and Abranchiata ; into the Allantoidea and Anallantoidea. 

159 It would be safe to say that any living Vertebrate with side fins sup¬ 
ported by fin-rays is a Fish; but the extinct Reptile Ichthyosaurus also had 
them. 

ieo u 'ph e ca p ac ity for growing as long as life lasts, which some Fishes are 
said to possess, may be explained by the facts that their bodies are, firstly, of 
very nearly the same specific gravity as the water in which they live, and, 
secondly, of a temperature which is but a very little higher than that which 
they are there exposed to. Thus the force which in other animals is ex¬ 
pended in the way of opposition to that of gravity and in the way of pro¬ 
ducing heat is available for sustaining continuous growth.”— Rolleston. 

161 Amphibians with a moist skin are also remarkable for their cutaneous 
respiration. They will live many days after the lungs are removed. Their 
vertebrae vary in form : in the lowest they are biconcave, like those of Fishes ; 
in Salamanders they are opisthocoelous: ?n the Frogs and Toads they are 
usually procoelous. 

162 Salamanders are often taken for Lizards, but differ in having gills in 
early life and a naked skin. The Proteus and Siren resemble a tadpole ar¬ 
rested in its development. 


394 


NOTES. 


163 The Surinam Toad has no tongue. 

164 The posterior pair of limbs is sometimes represented by a pair of small 
bones; and the Boas and Pythons show traces of external hind-limbs. 

165 There are some notable exceptions. The Slow-worm is legless, and 
the Chameleon has a soft skin, with minute scales. 

166 According to Owen; but Huxley insists that the plastron belongs to 
the exoskeleton. 

167 Knees always bend forward, and heels always bend backward. 

168 We cannot claim that this airy skeleton is necessary for flight. The 
bones of the Bat are free from air, yet it is able to keep longer on the wing 
than the Sparrow. The common Fowl has a hollow humerus; while some 
Birds of long flight, as the Snipe and Curlew, have airless bones. 

169 The fossil Archceopteryx , a lizard-like Bird, is placed in a separate di¬ 
vision, Saururce. Birds have also been divided according to their degree of 
development at birth into (1) Hesthoyenous, as Fowls, Ostriches, Plovers, 
Snipes, Rails, Divers, and Ducks, whose chick is hatched completely clothed, 
has perfect senses, runs about, and feeds itself. When full grown, it uses its 
feet rather than wings, flying with a rapid, labored stroke, and taking the 
first opportunity to settle on land or water, not on trees; the male is po¬ 
lygamous and pugnacious; the female makes little or no nest: and neither 
sex sings. This group is of the best use to man, and approaches more near¬ 
ly to Mammals, the habitual use of the legs and preference for land or water 
degrading it as a Bird and raising it in the list of animals; (2) Gymnogenous, 
as Gulls, Pelicans, Birds of Prey, Herons, Sparrows, Woodpeckers, and 
Pigeons, whose chick comes helpless, blind, and naked; it can neither walk 
nor feed itself, but gapes for food; the adult is monogamous, and builds 
elaborate nests in trees and perches ; many sing; all are habitual fliers. 
These are birds par excellence , gifted with higher intelligence than the 
others, and are never domesticated for food. 

170 Hopping is characteristic of and confined to the Perchers; but many 
of them, as the Meadow-lark, Blackbird, and Crow, walk. 

171 This order is artificial. But it is better to retain it until ornithologists 
agree upon some natural arrangement. The classification of birds is taken 
from Coues’s “Key to North American Birds,” as being the work on orni¬ 
thology in most general use. 

172 The Whales are hairy during foetal life only. 

173 The Manati has 6; Hoffmann’s Sloth 6 ; and two species of three-toed 
Sloth have respectively 8 and 9. 

174 As in the Whale, Porpoise, Seal, and Mole. Teeth are wanting in the 
Whalebone Whales, Ant-eaters, Manis, and Echidna. 

175 The Monotremes resemble Marsupials in having marsupial bones, but 
have no pouch. They differ from all other Mammals in having no distinct 
nipples. 

176 The pouch is wanting in some Opossums and the Dasyurus. 

177 For the best account of the Elephant, see Tennant’s “Ceylon” or 
Brehm’s “Thierleben.” 

178 The fore-feet of the Tapir have four toes, but one does not touch the 
ground. 


NOTES. 


395 


179 The extinct Horse ( Hipparion ) had three toes, two small hoofs dangling 
behind. The foot of the Horse is of wonderful structure. The bones are 
constructed and placed with a view to speed, lightness, and strength, and 
bound together by ligaments of marvellous tenacity. There are elastic pads 
and cartilages to prevent jarring; and all the parts are covered by a living 
membrane which is exquisitely sensitive, and endows the foot with the sense 
of toucl), without which the animal could not be sure-footed. The hoof 
itself is a world of wonders, being made of parallel fibres, each a tube com¬ 
posed of thousands of minute cells, the tubular form giving strength. There 
are three parts, ‘•wall,” “sole,” and “frog”—the triangular, elastic piece 
in the middle, which acts as a cushion to prevent concussion and also 
slipping. 

180 The Camel and Llama are exceptional, having two upper incisors and 
canines, are not strictly cloven-footed, having pads rather than hoofs, and 
are hornless. 

181 The Hyena alone of the'Carnivores has only four toes on all the limbs, 
and the Dog has four hind-toes. The Lion is the king of beasts in majesty, 
but not in strength. Five men can easily hold down a Lion, while it re¬ 
quires nine to control a Tiger. 

182 The eye-orbits of the Lemurs are open behind. The Flying Lemur 
(Galeopithecus) is considered an Insectivore. 

183 The old term Quadruinana is rejected because it misleads, for Apes, as 
well as Men, have two feet and two hands. There is as much anatomical 
difference between the feet and hands of an Ape as between the feet and 
hands of Man. Owen, however, with Cuvier, considers the Apes truly “four- 
handed.” 

184 It fails to cover in the Howling Monkey and Siamang Gibbon; but in 
the Squirrel Monkey it more than covers, overlapping more than in Man. 
As to the convolutions, there is every grade, from the almost smooth brain 
of the Marmoset to that of the Chimpanzee or Orang, which falls but little 
below Man’s. 

185 The tailed Apes of the Old World have longer legs than arms, and 
generally have “ cheek-pouches,” which serve as pockets for the temporary 
stowage of food. 

186 In the human infant, the sole naturally turns inward; and the arms 
of the embryo are longer than the legs. 

187 The Aye-aye, the lowest of the Lemurs, is remarkable for the large 
proportion of the cranium to the face. 

188 This feature was shared by the extinct Anoplotheriuvi , and now to 
some extent by one of the Lemurs ( Tarsius ). 

189 We have treated Man zoologically only. His place in Nature is a 
wider question than his position in Zoology; but it involves metaphysical 
and psychological considerations which do not belong here. 

190 See Lewes’s charming “Studies in Animal Life.” Doubtless an ex¬ 
amination of all the strata of the earth’s crust would disclose forms im¬ 
mensely outnumbering all those at present known- And even had we every 
fossil, we w'ould have but a fraction of the whole, for many deposits have 
been so altered by heat that all traces have been wiped out. Animal life is 


396 


NOTES. 


much more diversified now than it was in the old geologic ages; for several 
new types have come into existence, and few have dropped out. 

191 Among the types characteristic of America are the Gar-pike, Snapping- 
turtle, Hummers, Sloths, and Musk-rat. Many of our most common animals 
are importations from the Old World, and therefore are not reckoned with 
the American fauna; such as the Horse, Ox, Dog and Sheep, Rats and 
Mice, Honey-bee, House-fly, Weevil, Currant-worm, Meal-worm, Cheese- 
maggot, Cockroach, Croton-bug, Carpet-moth and Fur-moth. Distribution 
is complicated by the voluntary migration of some animals, as well as by 
Man’s intervention. Besides Birds, the Bison and Seals, some Rats, certain 
Fishes, as Salmon and Herring, and Locusts and Dragon-flies among In¬ 
sects, are migratory. 

192 When the cable between France and Algiers was taken up from a depth 
of eighteen hundred fathoms, there came with it an Oyster, Cockle-shells, 
Annelid tubes, Polyzoa, and Sea-fans. Ooze brought up from the Atlantic 
plateau (two thousand fathoms) consisted of ninety-seven per cent, of Fora- 
minirers. 


THE NATURALIST'S LIBRARY. 


The following works of reference, accessible to the American student, 
are recommended: 


General Works and Text-books. 

Agassiz, Methods of Study in Natural 
History. 

Agassiz and Gould, Principles of Zool¬ 
ogy. 

Rolleston, Forms of Animal Life. 

Lewes, Studies of Animal Life. 

Jones, General Outline of the Organiza¬ 
tion of the Animal Kingdom. 

Htjxley and Martin, Elementary Biol¬ 
ogy. 

Owen, Comparative Anatomy of Inverte¬ 
brates and Vertebrates. 

Van der Hoeven, Handbook of Zoology. 

Wood, Illustrated Natural History. 

Nicholson, Manual of Zoology. 

Tenney, Elements of Zoology. 

Morse, First Book of Zoology. 

Jones, Animal Creation. 

Packard, Zoology. 

Gegenbaur, Comparative Anatomy. 

Invertebrates. 

Huxley, Anatomy of Invertebrated Ani¬ 
mals. 

Macallister, Introduction to Animal 
Morphology. 

Brooks, Handbook of Invertebrate Zool¬ 
ogy- 

Siebold, Anatomy of Invertebrates. 

Vertebrates. 

Huxley, Anatomy of Vertebrated Ani¬ 
mals. 

Macallister, Morphology of Vertebrates. 

Huxley and Hawkins, Atlas of Compar¬ 
ative Osteology. 

Flower, Osteology of Mammalia. 

Ciiauveau, Comparative Anatomy of Do¬ 
mesticated Animals. 

Mtvart, Lessons in Elementary Anatomy. 


Mivart, The Cat. 

Gray, Anatomy, Descriptive and Surgical. 
Striokee, Handbook of Human and Com¬ 
parative Histology. 

Embryology. 

Balfour, Comparative Embryology. 
Foster and Balfour, Elements of Embry¬ 
ology. 

Packard, Life Histories of Animals. 
Physiology. 

Carpenter, Comparative Physiology. 
Huxley, Lessons in Elementary Physiol¬ 
ogy. 

Foster, Text-book of Physiology. 
Martin, The Human Body. 

Flint, Physiology. 

Geographical Distribution. 
Wallace, Geographical Distribution of 
Animals. 

Murray, Geographical Distribution of 
Mammals. 

Microscopy. 

Carpenter, The Microscope and its Rev¬ 
elations. 

Griffiths and Henfrey, The Micrograpb- 
ic Dictionary. 

Darwinism. 

Schmidt, Descent and Darwinism. 
Haeckel, History of Creation. 

Darwin, Origin of Species. 

Huxley, Lay Sermons, etc. 

Mivart, Lessons from Nature. 

Special Works. 

Clark, Mind in Nature. 

Agassiz, Sea-side Studies in Natural His* 
tory. 





398 


THE NATURALIST’S LIBRARY. 


Taylor, Half-hours at the Sea-side. 

Greene, Manuals of Sponges and Coelen- 
terata. 

Dana, Corals and Coral Islands. 

Vereill and Smith, Invertebrates ofVine- 
yard Sound. 

Gould and Binney, Invertebrata of Mas¬ 
sachusetts. 

Woodward, Manual of Mollusca. 

Packard, Guide to the Study of Insects. 

Duncan, Transformations of Insects. 

Stoker, Fishes and Reptiles of Massachu¬ 
setts. 


Coues, Key to North American Birds. 
Jordan, Popular Key to the Birds, etc., 
of Northern United States. 

Baird, Brewer, and Ridgway, Birds of 
North America. 

Baird, Mammals of North America. 
Allen, Mammalia of Massachusetts. 
Soammon, Marine Mammals of North Pa¬ 
cific. 

Pkschel, The Races of Man. 

Marsh, Man and Nature. 

Tyloii, Primitive Culture. 

Nicholson, Palaeontology. 


Of serial publications, the student should have access to the American 
Naturalist , American Journal of Science , Popular Science Monthly , Smith¬ 
sonian Contributions and Miscellaneous Collections , Bulletins and Proceed¬ 
ings of the various societies, Annals and Magazine of Natural History , and 
Nature. 

The following German works are recommended as having no English 
equivalents : 


Claus, Grundzuge der Zoologie. 
Payenstechek, Allgemeine Zoologie. 
Bronn, Classen und Ordnungen des Thier- 

Also the periodicals— 

Zoologischer Anzeiger. 


reichs (unfinished and expensive, but 
indispensable to the working zoolo¬ 
gist). 


Biologisches Centralblatt. 







INDEX. 


In the Index the numbers in Roman type (21) refer to pages; those in bold-faced 
type (40) refer to cuts. No attempt is made to analyze the statements made for 
each group in Part II. Reference is made for each class or prominent order to those 
cuts in Part I. which illustrate the group. 


Absorption, Invertebrates, 94. 

“ Vertebrates, 94, 60, 61. 

Acaleph®, 247. 

“ see Jelly-fish. 

Acarina, 237, 268. 

Acarus, 2S7. 

Acetabulum, 147. 

Acipenser, 315, 290. 

Acorn-shell, 284, 254. 

“ see Barnacle. 

Acrania, 309, 310, 282. 

Actiuaria, 251, 199, 201-206. 

Actinoid Polyp, 251, 199. 

“ anatomy of, 38, 95, 198. 

“ blood of, 97. 

“ development of, 205, 208. 

“ liver-cells of, 124. 

“ mouth of, 55, 199. 

“ nettle-cells of, 51. 

“ prehension of, 51. 

“ reproduction of, 192. 

“ respiration of, 112. 

“ skeleton of, 130, 95. 

“ skin of, 127. 

Adder, 320, 298. 

Adipose Tissue, 33, 10. 


^Eolis, 274. 

Air-bladder, 117. 

Albatross, 330. 

Albumen, 19. 

Alcyonaria, 256, 200, 207 , 208. 
Alcyonium, 256, 208. 

Alimentary Canal, 74. 

Coelenterata, 75. 
Crustacea, 76. 
development of, 203. 
duodenum, 90. 
Echinoderms, 76. 
Fishes, 80. 

Insects, 78. 


Alimentary Canal, Mammals, 35. 


(t 

“ microscopic anatomy 


of, 57, 58. 

a 

“ Mollusks, SO. 

<« 

“ Protozoa, 74. 

it 

“ Spiders, 79. 

n 

“ stomach, S7. 

c< 

“ structure of, 89. 

(i 

“ see Intestine, Mouth, 


Stomach, Teeth. 

Allantoidea, 393. 


Allantois, 117, 203, 169-171. 

Alligator, 324, 303. 

“ nest, 196. 

Alternate generation, 212. 

Ambulacra, 131. 

Ammonite, 279. 

Amnion, 202, 170, 171 
Amoeba, 241,185. 

“ conjugation of, 196. 

“ ectosarc of, 75. 

“ feeding of, 55. 

“ locomotiou of, 154,157. 
Amphibia, 317, 63, 65, 76, 85, 87, 294- 
296 

“ blood of, 99, 63-65. 

“ brain of, 172, 140. 

“ circulation of, 108, 76. 

“ lungs of, 118. 

“ mouth of, 61. 

“ see Frog. 

Amphicoelous, 386. 

Amphioxus, 310, 282. 

“ feeding of, 50. 

“ skeleton of, 139. 

Amphithoe, 284, 252. 

Analogy, 21S. 

Anchylosis, 143. 

Animal, defined, 22. 

Animalcule, see Protozoa. 












400 


INDEX. 


Annelides, 2C8,17, 223. 

Anodou, 78; see Clam. 

Anoura, 31S. 

Ant, 304. 

Ant-eater, 344, 338. 

Antennae, 177,147. 

Anthozoa, 250, 38, 95, 198, 208. 

Ape, 357, 120, 353-357. 

Apis, 304, 277. 

Aplysia, 274. 

Apteryx, 327. 

Arachnida, 2S7. 

“ see Centipede, Scorpion, Spi¬ 
der. 

Araneina, 289, 18, 25, 260, 261. 

“ see Spider. 

Arden, 332, 313. 

Areuicola, 113, 77. 

Areolar Tissue, 35, 3. 

Argouauta, 2S0, 249. 

Armadillo, 135, 344, 101, 834. 

Artery, 104. 

Arthropods, 281. 

“ blood of, 99. 

“ development of, 205. 

“ number of, 221. 

“ skin of, 127. 

“ see Crab, Insect, Lobster, My- 

riapoda, Spider. 

Ascidian, 305, 278, 279. 

“ circulation of, 107. 

“ mouth of, 60. 

“ skin of, 127. 

Astacns, 2S3, 250. 

Asterias, 260. 

“ see Starfish. 

Asteroidea, 258, 126, 183, 212, 213. 
Astrsea, 252, 203. 

Astrophyton, 200. 

Atavism, 216. 

Attacus, 302, 274. 

Auger-shell, 270, 288. 

Auk, 329. 

Aurelia, 24S, 195. 

“ see Jellv-fish. 

Aves, 325, 50, 65, 76, 105, 116, 125, 162, 
170 

Bauirusa, 69, 34. 

Baboon, 359. 

Balaena, see Whale. 

Balanus, 2S4, 254. 

Barnacle, 284, 253, 254. 

“ metamorphosis of, 210. 

“ mouth of, 57. 

“ see Cirripedia. 

Basket-fish, 260. 

Batrachia, 31S, 63, 65, 76, 85, 87, 296,297. 

“ see Frog. 

Bats, 346, 33*, 340. 

Beaver. 346, 337. 


Bed-bug, 297. 

Bee, 303, 277. 

“ alimentary canal of, 42. 

“ eggs of, 195. 

“ eye of, 155. 

“ instincts of, 1S5. 

“ mode of feeding of, 50. 

“ mouth of, 59, 22. 

“ section of, 81. 

“ temperature of, 121. 

“ see Hymenoptera, Insecta. 

Beetle, 297, 267, 268. 

“ alimentary canal of, 41. 

“ development of, 297, 26£, 

“ eye of, 182, 156. 

“ mouth of, 57. 

“ skeleton of, 292, 262 

“ see Coleoptera, Insecta. 

Belemnite, 281. 

Bernicla, 310. 

Beroe, 257. 

Bile, 98. 

Bird-of-Paradise, 339. 

Birds, 325, 304-328. 

“ alimentary canal of, 84, 5Ci 
“ anatomy of, 50, 304. 

“ beak of, 54. 

“ blood corpuscles of, 99, 6*. 

“ brain of, 141. 

“ breathing of, 119. 

“ circulation of, 107, 76 
“ distribution of, 378. 

“ drinking of, 50. 

“ egg of, 193, 162. 

“ embryo of, 170. 

“ eye of, 184. 

“ feather of, 137, 204. 106. 

“ flight of, 160, 125. 

“ gizzard of, S4, 384, 50. 

“ heart of, 109. 

“ locomotion of, 1G6. 

“ lungs of, 118, 50. 

“ mouth of, 62. 

“ skeleton of, 143,116- 
“ smell of, 118. 

“ temperature of, 121. 

“ voice of, 189. 

“ wings of, 160, 304. 

Bivalve, see Clam, Lamellibranchiata 
Oyster. 

Blackbird, 339. 

Blastema, 33. 

Blastula, 198,165. 

Blood, 97. 

“ circulation of, 103. 

“ corpuscles, 98,99, 62-65. 

“ development of, 200. 

“ functions of, 97 
“ of Invertebrates, 97. 

“ rate of motion of, 111. 

“ temperature of, 100. 





INDEX. 


401 


Blood of Vertebrates, 98. 

“ vessels, 104. 

Blubber, 34S. 

Blueflsh, 312, 284. 

Boa, skull of, 72, 37. 

Boue, composition of, 147. 

“ development of, 203. 

“ structure of, 36, 7, 8. 

Bos, see Ox. 

Brachiopoda, 2GG, 221, 222. 
Brachycephalic, 393. 

Bradypus, 344. 

Brain, 170. 

“ case of, see Skull. 

“ development of, 204. 

“ functions of, 173. 

" parts of, 170. 

“ weight of, 170. 

Brain-coral, 232, 204. 

Bronchus, 119, 86. 

Bryozoa, see Polyzoa. 

Bubble-shell, 274, 231. 

Buccinum, 272, 228. 

Budding, 192. 

Bufo, 318. 

“ see Toad. 

Bugs, mouth of, 59. 

“ see Hemiptera. 

Bulimus, 275, 233. 

Bulla, 272, 231. 

Butterfly, 273. 

“ anatomy of, 43. 

“ metamorphosis of, 20S, 172. 

“ mimicry of, 217. 

“ mouth of, 59, 23. 

“ scales of, 271, 272. 

Caddis-fcy, 295. 

Ctecilia, 318. 

Caecum, 51. 

Calcispongia, 246. 

Camel,.352. 

Cameo-shell, 278, 237. 

Canaliculi, 37, 8. 

Canine teeth, G9, 34, 35. 

Capillaries, 104, 66, 68. 

Caprimulgus, 338, 323. 

Capybara, 346. 

Carapace, 323,115. 

Cardinal, 227. 

Carinatae, 32S. 

Carnivora, 353, 90, 92, 106, 10S-110, 128, 
142, 346, 350. 

“ brain of, 142. 

“ teeth of, 70. 

Cartilage, 36, 5. 

Cassis, 278, 237. 

Cassowary, 327. 

Castor, 346, 337. 

Cat, 355. 

“ brain of, 142. 


Cat, teeth of, 70. 

Caterpillar, 301. 

“ anatomy of, 78, 40. 

circulation in, 105, 69. 

“ false legs of, 172. 

“ head of, 303, 276. 

“ heart of, 105, 69. 

“ jaws of, 53, 276. 

“ locomotion of, 162. 

“ muscles of, 156. 

“ nervous system of, 169, 130. 

“ see Butterfly, Iusecta, Lepi- 

doptera. 

Catfish, 316, 291. 

Cebus, 357, 352. 

Cell, 31, 1. 

Cement, 66, 31. 

Centipede, 291, 259. 

Cephalization, 225. 

Cephalopoda, 27S, 16, 47, 151, 247-249. 

“ see Cuttlefish, Squid. 

Cephalo-thorax, 282. 

Cerebellum, 171. 

Cerebrum, 170. 

Ceryle, 33S, 327. 

Cetacea, 348, 30, 341, 342. 

“ see Whale. 

Chalaza, 193,162. 

Chameleon, 322. 

“ tongue of, 81. 

Cheiroptera, 346, 339, 340. 

Chelonia, 322,115, 301, 302. 

“ see Turtle. 

Chelydra, 323. 

Chilognatha, 291. 

Chilopoda, 291, 259. 

Chimsera, 314. 

Chimpanzee, 357, 354, 356. 

“ skeleton of, 120. 

“ teeth of, 35. 

Chitine,132. 

Chiton, 276, 24ft 

Chlorophyl, 23. 

Choroid, 183. 

Chrysaora, 213,178. 

Chrysalis, 20S, 390,172. 

Chyle, 93, 59. 

Chyme, 92. 

Cicada, 297, 266. 

Cicatricula, 194. 

Cidaris, 262, 96, 97. 

Cilia, 154, 2. 

Ciliata, 24S, 188. 

Circulation in Arthropoda, 106. 

“ in Ascidians, 107. 

“ in Birds, 109. 

11 development of, 200. 

“ in Echiuodermata, 105. 

“ in Insects, 105. 

“ in Mammalia, 109. 

“ in Mollusca, 106. 


26 







INDEX. 


402 


Circulation in Vermes, 105. 

“ in Vertebrata, 107, 281. 

“ see Heart. 

Cirripedia, 284, 253, 251. 

“ see Barnacle. 

Clam, 272. 

“ adductors of, 46. 

“ alimentary canal of, 80, 44,46. 

“ anatomy of, 46. 

“ circulation in, 106. 

“ ear of, 178,150. 

“ foot of, 161, 46. 

“ gills of, 113, 78. 

“ heart of, 106, 46. 

“ hinge of, 270. 

“ locomotion of, 161. 

“ mouth of, 56. 

“ nervous system of, 168, 135. 

“ prehension of, 50. 

“ shell of, 133, 99. 

“ siphons of, 46. 

“ see Lamellibranchiata, Oyster. 

Clamatores, 33S, 322. 

Class, 235. 

Classification, 231. 

“ Table, 239. 

“ synopsis of, 362. 

Claws, 136, 

Cloaca, S5. 

Clypeaster, 262. 

Coagulation, 98. 

Cochineal, 297. 

Cockle, 272, 227. 

Cockroach, 297. 

Cod, 316, 292. 

“ eggs of, 195 

Ccelenterata, 246. 

“ number of, 221. 

see Actinoid Polyp, Hydra, 
Jelly-fish. 

Coleoptera, 297, 41, 156, 267, 268. 

“ see Beetle. 

Columbae, 323, 316. 

Condor, 335. 

Cone-shell, 270, 239. 

Conjugation, 196. 

Connective Tissue, 34, 3, 4. 

Coral, 130, 251, 95, 201-208. 

“ see Actinoid Polyp. 

Corallium, 256, 207. 

Coral reef, 254. 

Cormorant, 330, 309. 

Cornea, 1S3. 

Corpuscles, see Blood. 

Correlation, 318. 

Cowry, 276, 234. 

Corydalus, 295. 

Crab, 287, 257. 

“ locomotion of, 162. 

“ vocal organs of, 1S8. 

“ see Lobster. 


Crane, 332. 

Craniota, 309. 

Cranium, 141. 

Cray-fish, 282, 250. 

Cricket, 295, 264. 

Crinoidea, 258, 211. 

Crocodilia, 323, 803. 

“ exoskeleton of, Iba 
“ heart of, 108. 

“ locomotion of, 163. 

“ mouth of, 61, 26. 

skeleton of, 149, 11 a 
“ stomach of, 82, 49. 

“ see Reptilia. 

Crow, 339. 

Crustacea, 282. 

“ nauplius of, 211, 173 

“ see Crab, Lobster. 

Ctenactis, 253, 202. 

Ctenophora, 257, 209. 

Cuckoo, 335. 

Cuculi, 335, 321 

Curassow, 333. 

Cursores, 327, 335. 

Cuticle, 12S. 

Cutis, 128. 

Cuttlefish, 2S0, 248. 

“ anatomy of, 47. 

“ alimentary canal of, SO, 43o 

“ beak of, 52, 47. 

brain of, 168, 151. 

“ circulation in, 107. 

“ ear of, 151. 

“ eye of, 181, 151. 

“ heart of, 107. 

“ iuk-bag of, 47. 

“ mouth of, 57. 

“ pancreas of, 123. 

“ prehension of, 52. 

“ skeleton of, 134. 

“ suckers of, 16. 

“ Cephalopoda, Squid. 

Cyclops, 2S4, 255. 

Cypraea, 276, 234. 

Cypris, 2S4, 255. 

Cypseli, 335, 320. 

Daody-i.ong-i.kgs, 2S9,300. 

Daphnia, 284, 255. 

Dasypus, 344, 334. 

Dasyurus, 343. 

Decapoda (Crustacea), 286, 70, 248 259 
256, 257. 

(Dibranchiata), 2 * 0 . 

Decussation, 184. 

Deglutition, 72. 

Delphinus, 349, 343. 

Demodex, 2S7, 258. 

Dental Formulae, 70, 

“ Tissue, 38, 

Dentine, 38, 66, 31. 







INDEX. 


403 


Dermis, 128. 

Development, 197. 

“ by alternate generation, 211. 

“ of Bird, 199. 

“ of blastula, 198, 165. 

“ of embryonic forms, 207. 

“ of gastrula, 193, 166. 

“ of Invertebrates, 204. 

“ by metamorphosis, 207. 

“ by metamorphosis, retro¬ 

grade, 210. 

“ oviparous, 309. 

ovoviviparous, 309. 

“ segmentation of egg, 197. 

“ of Vertebrates, 205. 

“ viviparous, 309. 

“ see Metamorphosis, Repro¬ 

duction. 

Diaphragm, 86, 88. 

Diastema, 70, 383. 

Dibranchiata, 280, 16, 47,151, 248, 249. 

Differentiation, 31. 

Digestion, chemical, 92. 

“ of Invertebrate, 92. 

“ of Man, 93. 

“ object of, 91. 

“ of Vertebrate, 92. 

Digitigrade, 355, 128. 

Diploria, 254, 204. 

Dipnoi, 316, 293. 

Diptera, 300, 24, 127, 173, 269, 270. 

“ see Fly, Mosquito. 

Discophora, 220. 

Distribution, 371-379. 

Divers, 328. 

Dog, 354. 

“ brain of, 171. 
skull of, 143. 
teeth of, 68. 

Dolichocephalic, 393. 

Dolphin, 349, 343. 

“ teeth of, 68. 

Doris, 274. 

Dove, 333, 316. 

Dragon-fly, 294, 263. 

“ flight of, 387. 

Duck, 331, 311. 

Duck-mole, 342, 331. 

Dugong, 350. 

“ heart of, 73. 

Duodenum, 90. 

Eagle, 334, 319. 

Ear, 179, 387, 152. 

Ear-shell, 278, 235, 246. 

Earth-worm, 269. 

“ alimentary canal of, 77. 

“ circulation in, 105. 

“ locomotion of, 162. 

“ nervous system of, 168. 

“ prehension of, 52. 


Ecderon, 127. 

Echidna, 342. 

Echinodermata, 257. 

“ number of species of, 221 

Echinoidea, 261, 28,39, 96, 97, 214. 
Echinus, 262, 214. 

“ see Sea-urchin. 

Edentata, 344, 101, 333, 334. 

Egg, fertilization of, 197. 

“ form of, 195. 

“ number of, 195. 

“ segmentation of, 197, 165. 

“ structure of, 192, 161,163. 
Elasmobranchii, 314, 287, 288. 

“ see Ray, Shark. 

Elephant, 350. 

“ brain of, 170, 

“ foot of, 129. 

“ skeleton of, 119. 

“ teeth of, 69, 36. 

“ trunk of, 66. 

“ tusks of, 71, 66,119. 

“ voice of, 189. 

Elytra, 297. 

Embryology, 197. 

Emu, 327. 

Enamel, 66, 31. 

Encephalon, 170. 

Enderon, 127. 

Endoskeleton, 127 
Entomostraca, 2S4, 255. 

Epiblast, 199. 

Epidermis, 34. 

Epiglottis, 119, 159. 

Epithelium, 33, 2. 

Equus, see Horse. 

Euplectella, 246. 

Excretion, 121,125. 

Exoskeleton, 127. 

Eye, of Invertebrates, ISO. 

“ of Vertebrates, 181. 

“ development of, 204. 

Facial Angle, 309. 

Falcon, 335. 

Family, 235. 

Fat, 38, 10. * 

Feathers, 137,105. 

“ development of, 204. 

Felis, 355. 

Fertilization of Egg, 197. 

Fibrine, 98. 

Fishes, 310. 

“ air-bladder of, 117, 48. 

“ alimentary canal of, 80, 48. 

“ blood of, 99,100, 65. 

“ brain of, 172, 139. 

“ circulation in, 107, 51, 75. 

“ eye of, 184. 

“ fins of, 158, 123. 

“ gills of, 114, 48. 





INDEX. 


404 

Fishes, heart of, 108, 48. 

“ locomotion of, 159, 124. 

“ mouth of, 61. 

“ muscles of, 157, 48. 

“ number of species of, 313. 

“ ovary of, 48. 

“ pancreas of, 123. 

“ prehension of, 54. 

“ scales of, 135, 102, 288. 

“ skeleton of, 112. 

“ skull of, 13S, 112. 

“ teeth of, 61, 67, 32. 

Fish-hawk, 335, 318. 

Fission, 191, 160. 

Flagella, 154, 187. 

Flagellata, 243,187. 

Flamingo, 331. 

Flea, 300. 

Flight of Bats, 161. 

“ of Birds, 160. 

“ of Insects, 159* 

Fluke, 265. 

Flustra, 267, 220. 

Fly, 300. 

“ buzzing of, 188. 

“ foot of, 127. 

“ metamorphosis of, 270, 

“ mode of feeding of, 50* 

“ mouth of, 59, 24. 

“ see Diptera, Mosquito 

Fly-catcher, 338, 322. 

Flying Fox, 346. 

Follicle, 123, 90. 

Food, 47-49. 

Foramen magnum, 172. 

Foraminifera, 51, 241, 15, 186* 

Forms of animals, 222. 

Fox, 355, 349. 

Frog, 318, 297. 

“ alimentary canal of, 82. 

“ blood-corpuscles of, 99, 63, 65. 
“ breathing of, 119. 

“ circulation in, 108, 76. 

“ food of, 49. 

“ heart of, 10S. 

“ lungs of, 118, 85. 

“ lymph-heart of, 96. 

“ metamorphosis of, 209. 

“ respiration in, 117-119. 

“ skeleton of, 119,140,145, 87. 

“ tongue of, 61. 

“ vertebrae of, 140, 87. 

Fruit-moth, 303, 275. 

Function, 41. 

Fungia, 252, 202. 

Galt.-bi.adder, 124, 92. 

Gall-fly, 303. 

Ganglion, 166, 14, 146. 

Gannet, 331. 

Ganoidei, 315, 289, 290. 


Gar-pike, 315, 289. 

Gasteropoda, 20, 29,45,100,154,176, 272. 

“ see Snail. 

Gastric glands, 123, 90. 

“ juice, 93. 

Gastrula, 198, 166. 

Gavial, 324. 

Gecko, 322. 

Gelatine, 36. 

Genus, 235. 

Germinal vesicle, 192. 

Gibbon, 357. 

Gills, 114,125, 48. 

Giraffe, 353. 

Gizzard of Invertebrates, 7\ 

“ of Vertebrates, 84. 

Gland, 121, 89. 

“ gastric, 123, 90. 

“ liver, 123, 92. 

“ pancreas, 123, 91. 

“ salivary, 122. 

“ sweat, 126, 94. 

Globigerina, 242. 

Glottis, 119. 

Glycogen, 23. 

Goatsucker, 338, 32 3* 

Goniaster, 260, 212. 

Goose, 331, 310. 

Gorgonia, 256, 208. 

Gorilla, 357, 357. 

Grallatores, 332, 313. 

Grasshopper, 297. 

“ development of, 20& 

“ gizzard of, 79. 

“ mouth-parts of, 58, 24 

“ stridulation, 186. 

Grebe, 329. 

Gregarinida, 240,184. 

Grouse, 333, 315. 

Growth, 214. 

Grubs, 389. 

Gryllus, 295, 264. 

Guinea pig, 345. 

Gulls, 329. 

1 i *3SMATOORYA , 393. 

Hsematotherma, 393. 

Hasmocyanin, 102. 

Haemoglobin, 102. 

Hag-fish, 54, 314. 

Hair, 136, 94, 104. 

Hair-worm, 262. 

Haliotis, 278, 235, 244). 

Hand, 359. 

Hare, 346,336. 

Harvest-man, 289. 

Haversian Canals, 37, 7. 

Hawk, 335, 318. 

Hearing of Invertebrates, 178. 

“ of Vertebrates, 179. 

Heart, Arthropoda, 105,69, 70. 





INDEX. 


405 


Heart, development of, 200, 168. 

“ of Mollusks, 106. 

“ of Tunicates, 10T, 279. 

“ of Vertebrates, 107-109, 71-74. 
Heat, 121. 

Hedgehog, 346. 

Helix, 275, 232. 

Ilemiptera, 297, 265, 266. 

“ month of, 59. 

Heron, 332, 313. 

Heterocercal, 159, 123. 

Heteromya, 272. 

Hippopotamus, 352. 

“ foot of, 129. 
Histology, 12. 

Hog, 352. 

“ teeth of, 67. 

Holothuroidea, 262, 215. 

Homarus, see Lobster. 

Homo, see Man. 

Homocercal, 159, 287. 

Homology, 217. 

“ serial, 218. 
Homomorphism, 217. 

Hoofs, 136, 103. 

Hornera, 267, 220. 

Horns, 136. 

Horse, brain of, 171,13S. 

“ hoof of, 136,164, 103, 129. 

“ skeleton of, 151, 117. 

“ skull of, 144, 111. 

“ splint-bones of, 207. 

“ stomach of, 88, 53. 

Horse-fly, mouth of, 60, 24. 
Horseshoe-crab, 284. 

“ “ jaws of, 53. 

“ “ skeleton of, 131. 

Hummer, 335. 

Hyalea, 274, 229. 

Hydra, 246, 191. 

“ budding of, 192. 

“ digestive cavity of, 75. 

“ nerve-cells of, 168. 

“ repair of, 215. 

Hydroid, see Hydrozoa. 

Hydrozoa, 246,178, 191-196. 

“ development of, 205. 

“ metamorphosis of, 212. 

“ see Jelly-fish. 

Hyena, 355. 

Hymenoptera, 303, 22, 42, 81, 277. 

“ see Bee. 

Hypoblast, 199. 

Ibis, 332. 

Ichneumon, 304. 

Ichthyopsida, 309. 

Ichthyosaurus, 324. 

Idotia, 286, 251. 

Iguana, 322. 

Incisors, 68. 


Individual, 220. 

Infusoria described, 243, 160. 

“ digestive cavity of, 75. 

“ fissiou, 191,160. 

“ mode of feeding of, 50. 

“ motion of, 154. 

“ mouth of, 55. 

“ respiration of, 112. 

“ skin of, 127. 

Inheritance, 217. 

Iusectivora, 346. 

Insecta, 291. 

“ absorption of, 94. 

“ alimentary canal of, 79, 41-43- 
“ anatomy of, 43, 81. 

“ antennae of, 147. 

“ chrysalis of, 172. 

“ circulation in, 105, 292. 

• “ development of, 205. 

“ ear of, 179. 

“ eye of, 181, 155, 156. 

“ feet and legs of, 162, 127, 131. 

“ flight of, 159. 

“ gizzard of, 79. 

“ heart of, 105, 69. 

“ kidney of, 126, 41, 42. 

“ liver of, 124. 

“ locomotion of, 159,162. 

“ metamorphosis of, 207, 172, 173, 

264-267. 

“ mouth of, 57. 

“ mouth-parts of, 53, 21-24. 

“ muscles of, 156, 131. 

“ nervous system of, 169, 43 

“ respiration in, 114,291. 

“ salivary glands of, 122. 

“ silk glands of, 40. 

“ skeleton of, 132, 292, 98, 262. 

“ smell of, 178. 

“ spiracle of, 114, 79. 

“ touch of, 177, 147. 

“ tracheae of, 114, 40, 80, 81. 

“ wings of, 159. 

Insessores, 337, 322-328. 

Inspiration, modes of, 115,119,120. 

Instinct, 184. 

Intelligence, 187. 

Intestine of Amphibian, S2. 

“ of Bird, 84. 

“ of Fish, 81. 

“ of Mammal, 85. 

“ of Reptile, 82. 

“ see Alimentary Canal. 

Isomya, 272. 

Ivory, 66. 

Jaws, 51-71. 

Jay, 339. 

Jelly-fish, 247, 193-197. 

“ blood of, 97. 

“ development of, 212, 178, 19&. 



406 


INDEX. 


Jelly-fish, eye of, 180. 

“ mode of feeding of, 51. 

“ mouth of, 55. 

“ nerves of, 168. 

“ nettle-cells of, 51. 

“ reproduction of, 212. 

Joints, 147. 

Julus, 291. 

Kangaroo, 88,343. 

Kidney, 126, 41, 93. 

King-crab, see Horseshoe-crab. 
Kingfisher, 335, 327. 

Kite, 335. 


Labium and Labrum, 58, 21. 
Labyriuthodontia, 318. 

Lacerta, 321, 300. 

Lacertilia, 321. 

Lachnosterna, 297, 267. 

Lacteals, 94, 60. 

Lacunae, 37, 8. 

Lamellibranchiata, 270, 44, 46, 78, 09, 
135, 150, 224-227 
“ eye of, 181, 153. 

“ see Clam. 

Lamellirostres, 331, 311. 

Lamprey, 286. 

Lamp-shell, 266, 221. 

Lancelet, 310, 282. 

Land-snail, 275, 232. 

Lark, 340. 

Larynx, 189,159. 

Lasso-cells, 51. 

Leech, 268. 

“ alimentary canal of, 77. 

“ jaws of, 64. 

“ locomotion of, 161. 

“ mode of feeding of, 50. 

Lemur, 355, 351. 

Lepas, 284, 253. 

Lepidoptera, 300, 43, 172. 

“ see Butterfly. * 

Lepidosiren, 317. 

Lepidosteus, 315, 289. 

Libellula, 294, 263. 

Life, distribution of, 372. 

“ duration of, 226. 

“ nature of, 28. 

“ struggle for, 227. 

Lightning-bug, 299. 

Ligula, 5S, 21. 

Likeness, 215. 

Limax, 275, 232. 

Limbs, development of, 204. 

“ skeleton of, 146. 

Limnaea, 275, 232. 

Limpet, 278, 245. 

Limulus, 284. 

1 “ see Horseshoe-crab. 


Lion, 355. 

“ foot of, 128. 

“ skeleton of, 106. 

“ stomach of, 88, 55. 

Liver, 123, 92. 

Lizard, see Lacertilia. 

Lobster, 106, 70, 256. 

“ alimentary canal of, 78. 

“ anatomy of, 2S2. 

“ circulation in, 106, 70. 

“ ear of, 179. 

“ eggs of, 196. 

“ gills of, 114. 

gizzard of^4. 

“ locomotion of, 158. 

“ moulting of, 132. 

“ mouth of, 57. 

“ prehension of, 53, 57. 

“ respiration in, 114. 

“ skeleton of, 131. 

Lob-worm, 77. 

Locomotion of Arthropoda, 162. 

“ of Birds, 160 

“ of Fishes, 15S. 

“ of Insects, 159. 

“ of Mollusks, 161. 

“ of Starfish, 161. 

“ of Vertebrates, 163. 

“ of Worms, 161. 

Locust, 297. 

Loligo, see Squid. 

Longipennes, 329, 308. 

Loon, 32S, 307. 

Louse, 297, 50. 

Lucernaria, 197. 

Lumbricus, see Earth-worm 

Lungs, function of, 125. 

“ of Snail, 116. 

“ surface of, 3S5. 

“ of Vertebrates, 117. 

Lymph, 102. 

Lymphatics, 94, 61. 

Lymph-heart, 96. 

Maotra, 271, 46, 226. 

Madrepore, 252, 201, 206. 

Madreporic plate, 258, 39. 

Maggots, 3S9. 

Mammalia, 309. 

“ alimentary canal of, 85. 

“ anatomy of, 87, 52. 

blood-corpuscles of, 99, 05. 
“ brain of, 171,138,142-145, 

“ circulation in, 109, 76, 281. 

“ digestion of, 92, 51. 

“ drinking of, 50, 

“ ear of, 179,152. 

“ egg of, 198,165. 

“ embryo of, 202,171. 

“ eye of, 183,157. 

“ hair of, 136,104. 











INDEX. 


407 


Mammalia, heart of, 109, 73, 74. 

locomotion of, 103. 
lungs of, 118, 86. 

“ mouth of, 62. 

“ palate of, 86, 27, 51. 

placenta of, 190, 203,171. 
respiration in, 120. 
skeleton of, 139. 

“ smell of, 178,149. 

“ teeth of, 6S. 

“ touch of, 177. 

“ voice of, 189,159. 


Man, 359. 

“ blood-corpuscles of, 99, 62. 

“ brain of, 170,171,137,144,145. 
“ digestive tract of, 51. 

“ ear of, 179,152. 

“ eye of,19S, 157. 

“ mouth of, 86, 27. 

“ muscles of leg of, 165, 130. 

“ nose of, 178,149. 

Manatee, 350, 343. 

Mandibles, 5S, 21. 

Mantis, 53. 

Mantle, 127, 46. 

Marsipobranchii, 314, 2S6. 
Marsupialia, 342, 332. 

Mastodon, 350. 

May-fly, 295. 

Meandrina, 252. 

Medulla oblongata, 172. 

Medusa, see Jelly-fish. 

Megatherium, 344. 

Melania, 278. 

Menobranchus, 317, 294. 

Mesentery, S3. 

Mesoblast, 199. 

Metamorphosis, 207. 

“ of Crab, 209. 

“ of Frog, 209. 

“ of Insect, 208. 

“ of Grasshopper, 208. 

“ of Starfish, 20S. 


Metazoa, 244. 

Millepede, see Myriapoda. 

Millepore, 391. 

Mimicry, 217. 

Minerals and Organisms, 19. 

Mite, 287, 258. 

Molar Teeth, 69. 

Mole, 346. 

Mollusea, 269. 

“ absorption of, 94. 

“ anatomy of, 45, 46, 47, 78. 

“ circulation in, 106. 

“ development of, 205. 

“ digestion of, 92. 

“ distribution of, 377. 

“ growth of, 214. 

“ kidney of, 126, 78. 

“ liver of, 124. 


Mollusca, locomotion of, 161. 

“ metamorphosis of, 269. 

“ mode of feeding of, 52. 

“ mouth of, 56. 

“ nervous system of, 168,134,135, 

151, 157. 

“ number of species of, 221. 

“ respiration in, 113, 46, 47, 78. 

“ salivary glands of, 122. 

“ shell of, 133, 385, 99, 100. 

“ skin of, 127. 

“ see Clam, Cuttle - fish, Snail,, 

Squid. 

Monad, 243,187. 

Monera, 240,183. 

Monkey, 356, 19, 352. 

see Primates. 

Monomya, 271. 

Monotremata, 342, 331. 

“ mouth of, 62. 

Mosquito, 300,173, 269. 

“ metamorphosis of, 208. 

“ mode of feeding of, 50. 

Moth, 302, 274-276. 

“ anatomy of, 79, 43. 

“ metamorphosis of, 274. 

“ see Butterfly, Lepidoptera. 

Motor Nerves, 167. 

Moulting, 12S, 209. 

Mouse, 346. 

Mouth, 55. 

“ of Arthropoda, 57. 

“ of Ascidia, 60. 

“ of Birds, 62. 

“ of Ccelenterata, 55. 

“ of Echinodermata, 56. 

“ of Fishes, 61. 

“ of Infusoria, 55. 

“ of Mammals, 62. 

“ of Mollusks, 56. 

“ of Parasites, 55. 

“ of Reptilia, 61. 

“ of Vermes, 57. 

** of Vertebrata, 60. 

Mucous Membrane, 89 

Mud-fish, 315. 

Murex, 27S. 

Mus, 346. 

Musca, see Diptera, Fly. 

Muscle, 39,12,122. 

“ development of, 204. 

“ of Invertebrates, 156. 

“ kinds of, 155. 

“ of Vertebrates, 156. 

Mushroom-coral, 252, 202. 

Mussel, 270, 225. 

Myriapoda, 290, 259. 

“ alimentary canal of, 77 

“ mouth of, 57. 

respiration in, 116. 

“ see Centipede. 











408 


INDEX. 


Myrmecophaga, 344, 333. 

Mytilus, 270, 225. 

N ULS, 135. 

Narwhal, 223, 68. 

Natatores, 328. 

Natica, 27S. 

Natural Selection, 227, 

Nauplius, 211,177. 

Nautilus, 279, 247. 
Nematelminthes, 265, 218. 
Nereis, 268, 17. 

Nerve-cells, 40,132. 

“ fibres, 40, 13. 

“ kinds of, 167. 

“ velocity of impulse of, 167. 
Nervous System, 16S. 


(< 

44 

of Arthropoda, 169. 

(4 

44 

Brain, 170. 

(4 

44 

development of, 199, 67 

44 

44 

of Mollusks, 168. 

44 

44 

Spinal Cord, 175. 

44 

44 

of Starfish, 168. 

44 

44 

Sympathetic, 175,116. 

44 

44 

of Vertebrates, 169. 

44 

44 

of Worms, 168. 


Neuroptera, 294, 263. 

“ see Dragon-fly. 
Neuroskeleton, 141. 

Newt, 318, 296. 

Nomenclature, Zoological, 236. 
Notochord, 200, 167. 

Nucleolus, 31,1. 

Nucleus, 31,1. 

Nummulite, 242. 

Nutrition, 45. 

Nymph, 377. 

Ocelli, 1S1. 

Octopus, 2S0. 

(Esophagus, S6. 

Olfactory Lobes, 172. 

“ Nerves, 17S. 

Olive-shell, 278. 

Oniscus, 2S6. 

Operculum, 114,134, 228. 

Ophidia, 320. 

“ see Snake. 

Ophiura, 260. 

Opisthobranchs, 274, 352, 239, 231. 
Opisthocoelous, 383. 

Opossum, 342, 332. 

Optic Lobes, 172. 

Orang-utan, 357, 353. 355. 

Order, 235. 

Organ, 41. 

Organization, 30. 

Organ-pipe Coral, 251, 200. 

Oriole, 339. 

Ornithorhynchus, 342, 331. 
Orthoceras, 287. 


Orthoptera, 217, 295, 21, 264. 

“ see Grasshopper. 
Orycteropus, 344. 

Oscines, 338. 

Osseous Tissue, see Bone. 
Ossification, 37, 203. 

Ostrea, 272. 

“ see Oyster. 

Ostrich, 327, 305. 

Otoliths, 178,156. 

Ovipositor, 293. 

Owls, 335, 317. 

Ox, alimentary canal of, 90. 

“ foot of, 352,129. 

“ teeth of, 352. 

“ see Ungulata. 

Oyster, anatomy of, 80, 44. 

“ development of, 205. 

“ eggs of, 195. 

“ heart of, 106, 44. 

“ mouth of, 56. 

“ prehension of, 50. 

“ respiration in, 113. 

“ see Clam, Lamellibranchiata. 

Palate, 61. 

Pallia! Sinus, 271, 99. 

Palpi, 58, 21. 

Paludina, 27S, 244. 

Pancreas, 123, 91. 

Pancreatic Juice, 93. 

Pangolin, 344. 

Paper Nautilus, 280, 249. 

Papilio, 303. 

Papillae, 12S, 148. 

Paramecium, 243,188. 

“ see Infusoria. 

Parrot, 337, 320. 

“ tongue of, 62. 

Partridge, 333. 

Patella, 278. 

Pavement-teeth, 67,. 32. 
Pearl-oyster, 224. 

Pectoral Arch, 146. 

Pedicellariae, 77, 97. 

Pedipalpi, 28S. 

“ see Scorpion. 

Pelias, 320, 298. 

Pelican, 331. 

Penguin, 329, 306. 

Pennatula, 256, 208. 

Pentacriuus, 258, 211. 

Pepsin, 93. 

Peptone, 93. 

Perch, skeleton of, 112. 

Perchers, 337. 

Periosteum, 138. 

Peristaltic Movement, 8a>. 
Periwinkle, 278. 

Petrel, 330. 

Petromyzon, 314, 286. 





INDEX, 


409 


Pharyngobranchii, 310,282. 

Pharynx, S5. 

Pheasant, 333. 

Phoca, 354. 

Physalia, 24G, 104. 

Physeter, 348, 341. 

“ see Whale. 

Picarife, 335 
Pici, 335, 320. 

Pigeon, 333, 310. 

Pinnigrade, 354,128. 

Pisces, 310, 48, 51, 05, 75, 102. 112, 123, 
124, 139, 283-293 
“ see Fish. 

Placenta, 196,171. 

Planaria, 264, 217. 

Plant, 22. 

“ food of, 25. 

“ functions of, 24. 

Plantigrade, 355, 128. 

Plant-louse, 297. 

Plasma of blood, 9S. 

Plastron, 323. 

Platyhelminthes, 264, 210, 217. 

“ see Tape-worm. 

Platyonychus, 2S7, 257. 

Pleurobrachia, 257, 209. 

Plover, 332. 

Poison-fangs, 68, 33. 

Polycistina, 242, ISO. 

Polyp, 250. 

“ see Actinia. 

Polyzoa, 266, 220. 

Pond-snail, 275, 232. 

Porcupine, 346. 

Porites, 252. 

Porpoise, 88, 349, 54. 

Portal circulation, 307, 3S5, 281 
Portuguese Man-of-war, 246,194. 
Potato-worm, 303. 

Poulpe, 2S0. 

Prairie Chicken, 333, 315. 

Primates, 356, 35,120,143-145, 352-358. 
“ brain of, 143-145. 

“ skeleton of Chimpanzee, 120. 

“ teeth of Chimpanzee, 35. 

“ see Ape, Man, Monkey. 
Proboscidea, 350, 36, 119,129. 

Proboscis of Butterfly, 59, 23. 

“ of Elephant, 62,119. 

Proccelous, 383. 

Prognathous, 393. 

Prosobranchs, 278, 234-246. 

Proteus, 318, 295. 

“ blood-corpuscle of, 99, 65. 
Protista, 21. 

Protoplasm, 31. 

Protopterus, 316, 293. 

Protozoa, 238. 

“ number of species of, 221. 

“ see Amoeba, Infusoria. 


Pseudopodia, 51,15. 

Pseudotriton, 31S, 296. 

Psittaci, 337, 320. 

Pteropoda, 274, 229. 

“ mouth of, 56. 

Pulmonates, 274, 232, 233. 

Pulse, 3S5. 

Pupil, 1S3,158. 

Pygopodes, 328, 306, 307. 

Quaduumana, 356. 

Raccoon, 355, 346. 

Radiates, 233. 

Radiolaria, 241, 186. 

Rail, 332, 314. 

Rana, see Frog. 

Range of Animals, 373. 

Rank of Animals, 224. 

Raptores, 334, 116, 317-319. 

Rasores, 332, 315. 

Rat, 346. 

Ratitse, 327, 305. 

Rattlesnake, 68, 33. 

Raven, 339. 

Ray, 314, 288. 

“ teeth of, 67, 32. 

Razor-shell, 272. 

Redstart, 338, 325. 

Repair, 215. 

Reproduction, 191. 

“ asexual, 191. 

“ by budding, 192. 

“ checks on, 227. 

“ by division, 191. 

“ rapidity of, 226. 

“ sexual, 192. 

Reptilia, 319. 

“ alimentary canal of, S8. 

“ brain of, 172,141. 

“ circulation in, 108. 76. 

“ corpuscles of, 99, 65 

“ distribution of, 378. 

“ lungs of, 118, 84. 

“ mouth of, 61. 

“ prehension of, 61. 

“ scales of, 135. - 
“ teeth of, 67. 

“ voice of, 1S9. 

“ see Crocodile, Lizard, Snake 
Turtle. 

Respiration, 111. 

“ in Crustacea, 114. 

“ in Echinoderms, 112. 

“ in Fishes, 114. 

“ in Insects, 114. 

“ in Mollusks, 113. 

“ rate of, 120. 

“ in Vertebrates, 117. 

“ in Worms, 113. 

Rete mucosum, 128. 





410 INDEX. 


Retina, 183,158. 

Rhea, 327. 

Rhinoceros, 351, 344. 

Rhizopoda, 240, 15, 185,186. 

“ skeleton of, 129. 

Rodentia, 345, 335, 336, 337. 

“ teeth of, 71, 335. 

Rotifera, 260, 219. 

“ jaws of, 64. 

Rudimentary Organs, 207. 

Ruminantia, 351. 

“ stomach of, SS, 56. 

“ see Ox, Ungulaia. 

Salamander, 31S, 296. 

“ metamorphosis of, 174. 

Saliva, function of, 93. 

Salivary Glands, 122. 

Salmon, 316, 285. 

Sand-flea, 284, 252. 

Sandpiper, 332, 312. 

Sarcolemma, 39, 204. 

Sauropsida, 309. 

Saururse, 394. 

Scales of Butterflies, 301, 272. 

“ of Fishes and Reptiles,135,102,283. 

Scallop, eye of, 181, 153. 

“ shell of, 272. 

Scapular Arch, 146. 

Scarabseus, 299. 

Scarf-skin, 128. 

Sclerobase, 129. 

Scleroderm, 129. 

Sclerotic, 183. 

Scolopendra, 291, 259. 

Scorpion, 28S, 259. 

“ mouth of, 60. 

“ respiration in, 116. 

Sea-anemone, see Polyp. 

Sea-blubber, 247. 

Sea-butterfly, 273, 229. 

Sea-fan, 256, 208. 

Sea-hare, 274. 

Seal, 355, 128. 

Sea-lemon, 274. 

Sea-lily, 25S, 211. 

Sea-lion, 355, 350. 

Sea-slug, 274. 

Sea-urchin, 262, 214. 

“ absorption by, 94. 

“ alimentary canal of, 76, 39. 

“ anatomy of, 39. 

“ circulation in, 105. 

“ digestion iu, 92. 

“ growth of, 214. 

“ mode of feeding, 52. 

“ mouth of, 56. 

“ respiration in, 112. 

“ shell of, 28. 

“ skeleton of, 130, 96. 

“ spines of, 130, 97. 


Sea-urchin, teeth of, 64, 28. 

Sea-worm, 268, 17, 223. 

Secretion, 121. 

“ see Gland. 

Segmentation of egg, 197, 16b. 
Self-division, 191, 100. 

Sensation, 176. 

Sense of hearing, 178. 

“ of sight, ISO. 

“ of smell, 177. 

“ of taste, 177. 

“ of touch, 176. 

Sense-organs, see Sense. 

“ development of, 264. 
Sensibility, 176. 

Sepia, 2S0, 248. 

Serpent, see Snake. 

Sertularia, 247, 192. 

Serum, 98. 

Setae, 269. 

Setophaga, 340, 325. 

Seventeen-year locust, 297, 26o. 

Shark, 314, 287. 

“ eggs of, 194, 164. 

“ gills of, 114, 287. 

“ skeleton of, 137, 145. 

Shells of Crustacea, 131. 

“ of Echinoderms, 130. 

“ of Mollusks, 133. 

Shoulder-girdle, 146. 

Shrew, 63, 346, 338. 

Shrimp, 286. 

Sight, of Arthropods, 181. 

“ of Ccelenterates, 180. 

“ of Mollusks, 181. 

“ of Vertebrates, 1S2. 

Silk-gland, 40. 

Silk-worm, 303. 

Simia, 35S, 353,. 355. 

Sinuses, 13S. 

Siphouophora, 248, 194. 

Siphuncle, 279, 247. 

Siren, 318. 

Sirenia, 349, 73, 343. 

“ see Dugong. 

Size of Animals, 221. 

Skeleton, of Arthropoda, 131. 
of Birds, 116, 144. 

“ of Ccelenterates, 130. 

“ of Echinoderms, 130. 

“ of Fish, 138, 144, 11‘A 

“ of limbs, 146. 

“ Lion, 139, 116. 

“ Mammals, 139, 106, 114, 11V 
120 . 

“ Mollusks, 133. 

“ Reptiles, 113, 115. 

“ of skull, 141, 108, 111. 

“ of Vertebrates, 13a 

“ of Whale, 114. 

“ see Exoskeleton. 






INDEX. 


411 


Skin of Invertebrates, 127. 

“ of Vertebrates, 128. 

Skull, 141. 

Slater, 2S4, 251. 

Slug, 274, 282. 

Smell, 177. 

Snail, 272. 

“ alimentary canal of, SO, 45. 

“ anatomy of, 45. 

“ circulation in, 106, 45. 

“ eye of, 181,154. 

“ gills of, 113. 

“ gizzard of, 64. 

“ heart of, 45. 

“ jaw of, 56, 20. 

“ larva of, 176. 

“ locomotion of, 161. 

“ lung of, 116, 274, 45^ 

“ mode of feeding, 52. 

“ mouth of, 56. 

“ nervous system of, 16S, 134,154. 
“ operculum of, 114, 134, 228. 

“ respiration in, 116, 45, 228. 

“ shell of, 133, 100, 228, 233-246. 
“ siphon of, 228. 

“ smell of, 178. 

“ teeth of, 65, 20. 

“ tentacles of, 176,154, 228. 

“ see Gasteropoda. 

Snake, 320, 298, 299. 

“ deglutition of, 73. 

“ locomotion of, 162. 

“ lungs of, 119, 84. 

“ poison apparatus of, 6S, 33. 

“ scales of, 135. 

“ skull of, 37. 

“ stomach of, 82. 

“ tongue of, 61. 

“ Vertebrae of, 140. 

“ voice of, 189. 

“ see Boa, Ophidia, Reptilia. 

Snapping-bug, 299. 

Snipe, 332. 

Solaster, 260. 

Somite, 392. 

Songsters, 338. 

Sorex, 346, 338. 

Sow-bug, 285. 

Sparrow, 339. 

Species, defined, 235. 

“ number of, 221. 

Sperm-whale, see Whale. 

Sphinx-moth, 303, 43. 

Spider, classification of, 2S9, 260. 

“ alimentary canal of, 79. 

“ appendages of, 25. 

“ circulation in, 106. 

“ fangs of, 53,18, 25. 

“ mouth of, 60, 25. 
k ‘ respiration in, 116. 

“ spinnerets of, 289, 25, 261. 


Spider, web of, 2S9, 260. 

Spinal column, 140. 

“ cord,175. 

Spinneret of Spider, 289, 261. 

“ of Caterpillar, 301, 276. 

Spiracle, 114, 79. 

Spongida, 244, 189, 190. 

alimentary canal of, 76. 

“ anatomy of, 189. 

“ egg of, 194, 163. 

feeding of, 50, 189. 

“ respiration in, 112. 

skeleton of, 129,190, 

Squash-bug, 297, 

Squid, 2S0. 

“ locomotion of, 158. 

“ see Cuttlefish. 

Squirrel, 346. 

Stag, 352, 345. 

Star-fish, alimentary canal of, 76,126. 
“ anatomy of, 126. 

circulation in, 105,126. 

“ classification of, 258. 

“ development of, 208. 

“ digestion in, 92. 

“ locomotion of, 161, 126. 

“ metamorphosis of, 207. 

“ mode of feeding of, 51. 

“ mouth of, 56. 

“ nervous system of, 168,133. 

“ respiration in, 112. 

“ see Echinodermata. 

Stilt, 332. 

Stomach, S2-89. 

“ digestion in, 93. 

Stork, 332. 

Stridulation, 188. 

Strombus, 278, 243. 

Struggle for Life, 226. 

Struthio, 327, 305. 

Sturgeon, 315, 290. 

Subkingdom, 233. 

Sun-fish, 247- 

Sun-star, 260. 

Survival of Fittest, 226. 

Suture, 147. 

Swallow, 340, 328. 

Swan, 331. 

Swift, 335. 

Swimmeret, 282. 

Symmetry, 222. 

Sympathetic nervous system, 175, 146 

Synovia, 147. 

T.enia, see Tape-worm. 

Tanager, 339. 

Tapetum, 184. 

Tape-worm, 264, 216. 

“ feeding of, 49. 

Tapir, 63, 351. 

Taste, 177.. 



412 


INDEX 


Teeth, of Amphibia, 6T. 

“ of Fishes, 61, 66, 67. 

“ of Invertebrates, 63. 

“ of Mammals, 68, 70. 

*■ of Reptiles, 67. 

“ structure of, 3S, 66, 9, 31. 

Teleostei, 315, 284, 290-292. 
Telsou, 282. 

Temperature of Animals, 121. 
Tendon, 36. 

Tentacie, 51. 

Tent-caterpillar, 303. 

Termes, 295. 

Terebra, 278, 238. 

Terebratula, 267, 222. 
Terebratulina, 267, 221. 

Termite, 295. 

Tern, 329, 308. 

Testudo, see Turtle. 

Tetrabranchs, 279, 247. 
Tetradecapods, 285, 251, 252. 
Thoracic duct, 95, 61. 

Thorax, 119, 88. 

Thoruback, 315, 288. 
Thousand-legged Worm, see Julus. 
Thrush, 340. 

Thylacinus, 343. 

Thyroid Cartilage, 1S9,159. 

Ticks, 288. 

Tissue, 33. 

Toad, 31S. 

Tongue, of Batrachians, 61. 

“ of Birds, 62. 

“ of Fishes, 61. 

“ of Insects, 50,58. 

“ of Mammals, 63. 

“ of Mollusks, 52. 

“ of Spiders, 60. 

Top-shell, 278, 242. 

Tortoise, 323, 302. 

“ see Turtle. 

Totipalmates, 330, 309. 

Toucau, 335. 

Touch, 176. 

Trachea, 119. 

Tracheae, 114, 40. 79, 80, 81. 
Trichina, 265, 218. 

Tridacne, 272. 

Trilobite, 284. 

Trionyx, 322. 

Triton, 31S, 296. 

Tritouian, 274, 230. 

Trochosphere, 211,175. 

Trochus, 278. 

“ embryo of, 211,176. 
Trogon, 335, 321. 

Tubipora, 252, 200. 

Tunicatn, 305, 278, 279. 

“ see Ascidiaus. 

Turbo, 278. 242. 

Turkey, 333. 


Turritella, 278. 

Turtle, 322, 301, 302. 

“ alimentary canal of, 82. 

“ breathing of, 119. 

“ mouth of, 61. 

“ shell of, 135. 

“ skeleton of, 115. 

“ see Chelonia. 

Tusks, 3S3. 

Types, 233. 


Ungulata, 351, 53, 56, 103, 111, 117, 118 
129,138, 344, 345. 
feet of, 129. 

Unio, 272. 

“ eggs of, 196. 

Univalve, see Snail. 

Urodela, 317, 294-296. 

Variation, 216. 

Variety, 235. 

Veins, 104, 67. 

Veliger, 211,176. 

Vena cava, 104. 

Venus, 272. 

Venus’-basket, 246. 

Vermes, 263, 17, 77,175. 

“ see Earth-worm, Worms. 

Vertebrae, development of, 203. 

“ kinds of, 140, 106, 107. 

“ number of, 140. 

Vertebrata, 306. 

“ absorption in, 94. 

“ alimentary canal of, SO. 

“ blood of, 98. 

“ brain of, 170. 

“ circulation in,10^., 281. 

“ development of, 205. 

“ digestion in, 92. 

“ ear of, 179. 

“ exoskeleton of, 134. 

“ eye of, 183. 

“ gastric glands of, 123. 

“ heart of, 107. 

“ kidney of, 126. 

“ liver of, 124. 

“ lungs of, 117. 

“ mode of feeding of, 54. 

“ mouth of, 60. 

“ muscles of, 156. 

“ nervous system of, 169. 

“ number of species of, 221. 

“ pancreas of, 123. 

salivary glands of, 122. 

“ skeleton of, 137. 

“ skin of, 128. 

“ stomach of, 80. 

“ teeth of, 66. 

“ tongue of, 60. 

“ see Bird, Crocodile, Fish, 

Frog, Mammal, Reptile. 








INDEX 


413 


Villi, 90, 68. 

Vinegar-eel, 265. 

Yireo, S40, 3*26. 

Vitelline Membrane, 193. 
Viviparous, 309. 

Vocal Cords, 1S9. 

Voice, of Invertebrates, 1S8. 

“ o f Ve rtebr a tes, 1S9. 
Volute, 2TS, 241. 

Vorticella, 243, 160. 

Vulture, 335, 116. 

Walking-stick, 29T. 

Walrus, 355, 383. 

Warbler, 340. 

Wasp, 304. 

Water-boatman, 297, 265. 
Water-fleas, 2S4, 255. 
Wax-wing, 340. 

Weasel, 355, 348. 

Weevil, 300. 

Whale, 34S, 341, 342. 

“ baleen of, 65, 30. 

“ brain of, 170. 

“ fat of, 39. 

“ mode of feeding of, 50. 

“ month of, 62. 

“ swimming of, 159. 

“ teeth of, 333. 

Whelk, 278, 228. 

“ see Snail. 

White Ant, 295. 


Windpipe, 119, 86. 

Wings, of Bats, 161, 339, 340. 

“ of Birds, 160, 304. 

“ of Insects, 159, 266. 

Wolf, 355, 347. 

Wombat, 343. 

Woodpecker, 335, 320. 

Worms, 263. 

“ absorption in, 94. 

“ alimentary canal of, 77. 

“ blood of, 98. 

“ eye of, 17. 

“ head of, 17. 

“ jaws of, 17. 

“ larva of, 175. 

“ locomotion of, 161. 

“ mouth of, 57. 

“ number of spenes of, 22'i c 

“ proboscis of, IV. 

“ reproduction in, 192. 

“ respiration of, 113, 77. 

“ skin of, 127. 

“ see Earth-worm. 

Wren, 340. 

Yolk, 192. 

Zoological analysis, 236. 

“ barriers, 375. 

“ history, 18. 

“ provinces, 37€> 

Zoology, 19. 


THE END 
























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